Offshore wind power hybrid dc transmission system, control method, electronic device and medium

Abstract

The present application relates to the technical field of direct current transmission system, and particularly relates to a kind of offshore wind power hybrid direct current transmission system, control method, electronic equipment and medium;The system includes offshore wind farm cluster, offshore converter station cluster, cross-station interconnection AC sea cable, cross-station interconnection DC sea cable, DC transmission sea cable and onshore converter station;The AC bus of first offshore converter station and second offshore converter station is electrically connected by cross-station interconnection AC sea cable;The DC side positive pole of second offshore converter station is connected with the DC side negative pole of first offshore converter station by cross-station interconnection DC sea cable, and constitutes the series boosting structure of DC side;The AC side of onshore converter station is used to access receiving end AC power grid.Through such a way, the technical problem that the prior art lacks cross-wind farm power coordination and mutual aid capability when dealing with multi-wind farm grid-connected scene is solved, and the overall operation economy and flexibility of system are improved.

Description

Technical Field

[0001] This invention relates to the field of DC transmission system technology, and in particular to an offshore wind power hybrid DC transmission system, control method, electronic equipment and medium. Background Technology

[0002] As the global energy structure accelerates its transition to clean and low-carbon energy, offshore wind power, as an important direction for large-scale renewable energy development, has seen its installed capacity grow rapidly, and wind farm clusters are expanding into deeper and more remote areas. Since offshore wind farms are typically far from onshore load centers and the main grid, traditional AC transmission technologies face challenges such as high line losses, high reactive power compensation requirements, and difficulty in ensuring voltage stability. Therefore, flexible DC transmission technology based on voltage source converters has become the main technical means for efficient and reliable transmission of offshore wind power.

[0003] In the field of offshore wind power DC transmission, existing technologies have formed a mainstream scheme based on point-to-point topology. This scheme typically consists of an independent dual-ended DC transmission channel formed by an offshore converter platform and an onshore converter station. With the intensive and large-scale development of offshore wind power, when multiple adjacent or neighboring offshore wind farms need to be connected to the grid, the existing point-to-point structure usually requires the construction of an independent transmission channel for each wind farm. This results in low utilization of the transmission corridor and significantly increases investment in submarine cables, converter station construction, and operation and maintenance costs. Simultaneously, the lack of effective electrical interconnection and power exchange mechanisms between wind farms and their transmission channels makes it difficult for the system to achieve cross-channel power support and optimized allocation when a wind farm experiences output fluctuations, channel power is limited, or a fault occurs. This restricts the overall operating efficiency and power supply reliability of offshore wind power clusters.

[0004] Currently, to improve the economy and flexibility of offshore wind power DC transmission systems, the industry has explored the use of hybrid converter valves to balance cost and performance. For example, prior art document 1 (application publication number CN116722573A) discloses an offshore wind power monopolar hybrid DC transmission system capable of DC negative voltage start-up. It employs a hybrid topology of diodes and flexible DC converter valves on the offshore side and thyristors and half-bridge flexible DC converter valves on the onshore side, aiming to reduce the construction cost of offshore platforms and achieve black-start capability. However, this technical solution still adheres to the traditional point-to-point, single-wind-farm-to-single-onshore transmission architecture. Its technical improvements focus on optimizing the composition and start-up method of the converter valves within a single transmission channel, failing to overcome the inherent limitation of multiple offshore wind farms and transmission channels being isolated from each other. Specifically, existing technologies suffer from two prominent problems: First, each offshore wind farm still relies on its own independent point-to-point transmission channels for power transmission. These channels are completely decoupled electrically, making it impossible to achieve interconnection and aggregation of power or the sharing and reuse of transmission channels. This results in low utilization rates of key transmission assets such as submarine cables and poor engineering economics. Second, in scenarios with multiple wind farms coexisting, the system lacks an effective mechanism for power coordination and dynamic optimization at the wind farm cluster level. When the output characteristics of a wind farm change or its transmission channel becomes abnormal, the system as a whole struggles to quickly rebalance power and provide fault support, thus affecting the flexibility and reliability of large-scale offshore wind farm grid-connected operation. These intertwined problems make existing point-to-point topology-based offshore wind power DC transmission technologies unable to meet the actual needs of efficient aggregation and coordinated transmission for deep-sea, large-scale, multi-site wind farm clusters. Therefore, existing offshore wind power DC transmission technologies lack cross-wind farm power coordination and mutual assistance capabilities when dealing with multi-wind farm grid-connected scenarios. Summary of the Invention

[0005] To address the aforementioned shortcomings or deficiencies, this invention provides an offshore wind power hybrid DC transmission system, control method, electronic equipment, and medium, which can solve the technical problem of the lack of cross-wind farm power coordination and mutual assistance capabilities in the context of multi-wind farm grid connection scenarios.

[0006] This invention provides a hybrid DC transmission system for offshore wind power, including an offshore wind farm cluster, an offshore converter station cluster, inter-station interconnection AC submarine cables, inter-station interconnection DC submarine cables, DC transmission submarine cables, and an onshore converter station.

[0007] Offshore wind farm clusters are connected to offshore converter station clusters via AC convergence submarine cables.

[0008] The offshore converter station cluster includes at least one first offshore converter station and at least one second offshore converter station.

[0009] The AC busbars of the first and second offshore converter stations are electrically connected via cross-station interconnection AC submarine cables.

[0010] The positive DC-side terminal of the second offshore converter station is connected to the negative DC-side terminal of the first offshore converter station via an inter-station interconnection DC submarine cable, forming a series boost structure on the DC side.

[0011] The DC transmission submarine cable includes a positive DC transmission submarine cable and a negative DC transmission submarine cable. The positive DC side of the first offshore converter station is connected to the positive DC transmission submarine cable, and the negative DC side of the second offshore converter station is connected to the negative DC transmission submarine cable. The far ends of the positive DC transmission submarine cable and the negative DC transmission submarine cable are connected to the DC side of the onshore converter station.

[0012] The AC side of an onshore converter station is used to connect to the receiving-end AC power grid.

[0013] The first offshore converter station is equipped with a passive converter valve and a voltage source converter valve connected in parallel, while the second offshore converter station is equipped with a voltage source converter valve.

[0014] According to a second aspect, the present invention provides a control method for an offshore wind power hybrid DC transmission system. This method, based on the offshore wind power hybrid DC transmission system described in the above embodiments, includes: In response to the system startup command, the system sequentially controls the voltage source converter valves in the onshore converter station, the first offshore converter station, the offshore wind farm cluster, the passive converter valves in the first offshore converter station, and the voltage source converter valves in the second offshore converter station to execute the system startup control steps.

[0015] After the offshore wind power hybrid DC transmission system is started up and connected to the receiving-end AC grid, the steady-state operation control steps are executed to control the voltage source converter valve in the first offshore converter station to operate in the grid-connected control mode, control the voltage source converter valve in the second offshore converter station to operate in the dynamic voltage control mode, and control the onshore converter station to operate in the DC voltage control mode.

[0016] According to a third aspect, the present invention provides an electronic device comprising: At least one processor; and a memory communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor, which are executed by the at least one processor to enable the at least one processor to execute any of the offshore wind power hybrid DC transmission system control methods in the embodiments of the present invention.

[0017] According to another aspect of the present invention, a non-transitory computer-readable storage medium storing computer instructions is provided, wherein the computer instructions are used to cause a computer to execute any of the offshore wind power hybrid DC transmission system control methods in the embodiments of the present invention.

[0018] The present invention provides a hybrid DC transmission system for offshore wind power, which is realized through the coordinated arrangement and connection of offshore wind farm clusters, offshore converter station clusters, inter-station interconnection networks (composed of AC submarine cables and DC submarine cables) and onshore converter stations. The system comprises an offshore converter station cluster, including at least one first offshore converter station and at least one second offshore converter station, serving as a power collection and conversion node for multiple offshore wind farms. An inter-station interconnection AC submarine cable is installed between the AC buses of the first and second offshore converter stations to establish synchronous communication between the AC systems of different offshore wind farms. The positive DC terminal of the second offshore converter station is connected to the negative DC terminal of the first offshore converter station via an inter-station interconnection DC submarine cable to construct a series boost structure on the DC side. The positive DC terminal of the first offshore converter station and the negative DC terminal of the second offshore converter station are connected to the DC side of the onshore converter station via a DC transmission submarine cable to achieve efficient long-distance transmission of boosted DC power. A passive converter valve and a voltage source converter valve are configured in parallel in the first offshore converter station, and a voltage source converter valve is configured in the second offshore converter station to meet the economic and active control requirements of different operating stages of the system.

[0019] In this technical solution, the present invention addresses the problem of low utilization rate of existing power transmission channels in the background art. By connecting at least two offshore converter stations in series on the DC side, multiple offshore wind farms can share the same set of DC transmission submarine cables and onshore converter stations, achieving power transmission channel reuse and solving the defects of low asset utilization and poor engineering economy caused by building separate point-to-point DC channels for each wind farm. Addressing the lack of cross-wind farm power coordination and mutual assistance capabilities in existing technologies, the present invention connects the offshore converter stations on the AC side with cross-station interconnection AC submarine cables and constructs a series boost electrical connection on the DC side. This provides a physical path for power interaction and redistribution between different wind farms, solving the drawback of isolated wind farms and their transmission channels, which cannot provide power support in case of uneven output or failure. Therefore, the technical solution of the present invention solves the technical problem of lacking cross-wind farm power coordination and mutual assistance capabilities in multi-wind farm grid connection scenarios, improving the overall operational economy and flexibility of the system. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the topology of an offshore wind power hybrid DC transmission system according to an embodiment of the present invention; Figure 2 This is a flowchart of a control method for an offshore wind power hybrid DC transmission system according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the multi-module integrated system flow and information management of an embodiment of the offshore wind power hybrid DC transmission system of the present invention; Figure 4 This is a schematic diagram of the complete signal chain from high-level control commands to low-level power device trigger pulses in an offshore wind power hybrid DC transmission system according to an embodiment of the present invention. Figure 5 This is a block diagram of the Vf grid control system of the voltage source converter valve applied to the first offshore converter station according to an embodiment of the present invention; Figure 6 This is a block diagram of the principle of a DC voltage and AC current coordinated control system applied to an onshore converter station according to an embodiment of the present invention; Figure 7 This is a block diagram of an electronic device used to implement embodiments of the present invention. Detailed Implementation

[0021] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0022] During the development of this invention, the inventors, through extensive experiments and data analysis, revealed the inherent connection between the clustered power transmission needs of multiple offshore wind farms and the insufficient economy and flexibility of existing point-to-point DC transmission architectures. When using the traditional "point-to-point" topology where a single wind farm corresponds to a single DC channel, there is a fundamental contradiction between the utilization rate of the transmission channel and the power exchange capability between wind farms, resulting in low overall system efficiency and high investment costs. Based on this discovery, the inventors innovatively proposed this technical solution, the core of which lies in constructing a cross-site DC interconnection topology between offshore converter station clusters. By connecting at least one first offshore converter station and at least one second offshore converter station in series on the DC side, a step-by-step increase in DC voltage and the interconnection and aggregation of power from multiple wind farms on the DC side are achieved. Furthermore, by setting up cross-site interconnection AC submarine cables on the AC side, combined with the parallel configuration of passive and voltage source converter valves in the first offshore converter station and the configuration of voltage source converter valves in the second offshore converter station, an optimized balance between cost, control flexibility, and operational reliability is achieved. This solution embodies the core inventive concept of "topology interconnection, voltage superposition, and valve group coordination."

[0023] Specifically, through engineering practice and techno-economic analysis of deep-sea multi-wind farm development scenarios, the invention team discovered that existing power transmission systems based on a single offshore converter platform suffer from technical deficiencies such as the inability to share transmission channels and the lack of power support pathways between wind farms. This invention addresses these shortcomings by designing a cluster structure comprising a first and a second offshore converter station. It utilizes inter-station interconnecting DC submarine cables to achieve series connection on the DC sides of the two stations, constructing a physical channel for power convergence and voltage boosting. Furthermore, by configuring inter-station interconnecting AC submarine cables, it electrically connects the AC buses of different offshore converter stations, providing unified voltage and frequency synchronization support for the system. Additionally, by employing passive converter valves and voltage source converter valves in parallel at the first offshore converter station, combined with voltage source converter valves at the second offshore converter station, it enhances the system's ability to actively construct grids and flexibly adjust while ensuring basic power transmission economics. This achieves efficient, coordinated, and reliable transmission of offshore wind power, solving the technical problems of low transmission channel utilization and lack of dynamic power mutual assistance capabilities between stations when multiple wind farms are connected to the grid.

[0024] Therefore, according to a first aspect, the present invention provides an offshore wind power hybrid DC transmission system, including an offshore wind farm cluster, an offshore converter station cluster, inter-station interconnection AC submarine cables, inter-station interconnection DC submarine cables, DC transmission submarine cables, and an onshore converter station.

[0025] Offshore wind farm clusters are connected to offshore converter station clusters via AC convergence submarine cables.

[0026] Among them, AC convergence submarine cable refers to AC transmission cable used to converge and transmit the electrical energy of multiple offshore wind turbines that are distributed in a decentralized manner to an offshore converter station.

[0027] Specifically, in an offshore wind farm cluster, the electrical energy output from several to dozens of wind turbines located in the same area is first collected by an on-site step-up transformer, and then transmitted to the corresponding offshore converter station via multiple AC collection submarine cables. For example, for an offshore wind farm with a total installed capacity of 500 MW, four 33 kV AC submarine cables can be used to collect the electrical energy generated by the wind turbines and transmit it to an offshore converter platform approximately 15 kilometers away.

[0028] The offshore converter station cluster includes at least one first offshore converter station and at least one second offshore converter station.

[0029] Among them, the first offshore converter station refers to a converter station equipped with a parallel structure of two types of converter valves: passive type and voltage source type; the second offshore converter station refers to a converter station equipped with at least a voltage source type converter valve.

[0030] Specifically, the offshore converter station cluster is used to receive AC power from different offshore wind farms, convert it into DC power, and then transmit it via long-distance DC submarine cables after power aggregation and voltage boosting through inter-station interconnection. For example, in a certain deep-sea wind power development area, a first offshore converter station can be set up to serve wind farm area A, and a second offshore converter station can serve wind farm area B, together forming an offshore converter station cluster.

[0031] The AC busbars of the first and second offshore converter stations are electrically connected via cross-station interconnection AC submarine cables.

[0032] Among them, the cross-station interconnection AC submarine cable refers to the submarine cable that connects the AC busbars of different offshore converter stations. Its main function is to realize electrical connection and synchronization, rather than to undertake the main power transmission.

[0033] Specifically, the submarine cable provides uniform voltage and frequency support for the offshore AC system, ensuring that the AC side electrical characteristics of the first and second offshore converter stations remain consistent, thus creating conditions for wind turbine grid connection and stable system operation. For example, a single 66kV AC submarine cable, 10 kilometers long, can be used to directly connect the 66kV AC busbars of the two offshore converter stations.

[0034] The positive DC-side terminal of the second offshore converter station is connected to the negative DC-side terminal of the first offshore converter station via an inter-station interconnection DC submarine cable, forming a series boost structure on the DC side.

[0035] Among them, the cross-station interconnection DC submarine cable refers to the submarine cable used to realize the electrical connection between different offshore converter stations on the DC side. It is a key channel for constructing a series boost structure and realizing power transmission.

[0036] Specifically, through this connection method, the first and second offshore converter stations form a series circuit on the DC side, allowing the DC output voltages of the two converter stations to be superimposed, thereby achieving a step-by-step increase in the system's DC voltage. For example, assuming the rated DC voltage of the first offshore converter station is... The rated DC voltage of the second offshore converter station is By connecting them in series, the DC transmission voltage to the landside can be increased to [a higher value]. .

[0037] The DC transmission submarine cable includes a positive DC transmission submarine cable and a negative DC transmission submarine cable. The positive DC side of the first offshore converter station is connected to the positive DC transmission submarine cable, and the negative DC side of the second offshore converter station is connected to the negative DC transmission submarine cable. The far ends of the positive DC transmission submarine cable and the negative DC transmission submarine cable are connected to the DC side of the onshore converter station.

[0038] Among them, DC transmission submarine cable refers to submarine cable used to transmit DC power collected and stepped up at sea to land over long distances, and adopts bipolar connection.

[0039] Specifically, the positive DC transmission cable carries the current from the beginning of the series structure (i.e., the positive terminal of the first offshore converter station), while the negative DC transmission cable carries the current flowing to the end of the series structure (i.e., the negative terminal of the second offshore converter station). Together, they form a complete DC power transmission circuit. For example, two cables can be used. The DC submarine cables, each 120 kilometers long, transmit offshore power to onshore converter stations.

[0040] The AC side of an onshore converter station is used to connect to the receiving-end AC power grid.

[0041] Among them, onshore converter stations refer to converter stations set up on land to invert direct current (DC) power from the sea into alternating current (AC) power and integrate it into the power grid; receiving-end AC power grid refers to the land-based high-voltage AC transmission network that receives electrical energy.

[0042] Specifically, the onshore converter station converts the DC power from the DC transmission submarine cable into industrial frequency AC power, which is then stepped up by an on-site transformer and connected to a 220kV or 500kV receiving-end AC power grid. For example, the onshore converter station can be built within a coastal converter station and connected to a nearby hub substation via a 220kV AC transmission line.

[0043] The first offshore converter station is equipped with a passive converter valve and a voltage source converter valve connected in parallel, while the second offshore converter station is equipped with a voltage source converter valve.

[0044] Specifically, passive converter valves, such as 12-pulse diode rectifier valves without active control capabilities, are used to perform basic power transmission tasks, thereby reducing the construction cost and size of offshore platforms. Voltage source converter valves, such as modular multilevel converters (MMCs) with fully controllable components and active control capabilities, are used to provide functions such as voltage construction, system startup, and flexible power adjustment. For example, in the first offshore converter station, a set of 12-pulse diode rectifier valves and a set of MMC converter valves based on full-bridge submodules can be installed in parallel; in the second offshore converter station, a set of MMC converter valves based on half-bridge submodules is installed.

[0045] Therefore, by utilizing the aforementioned offshore wind power hybrid DC transmission system, users can achieve the efficient transmission of electricity from multiple offshore wind farms to the onshore power grid through a shared DC channel after the DC side is interconnected, aggregated, and boosted in series. This improves the utilization rate of the transmission channel and enables power exchange and coordinated regulation between wind farms.

[0046] In another embodiment, such as Figure 1 This diagram illustrates the topology of a hybrid DC-DC transmission system for offshore wind power according to a specific embodiment of the present invention. The diagram specifically shows the main hardware components and electrical connections of the system. Figure 1 The system includes a first offshore wind farm and a second offshore wind farm, which are connected to their respective No. 1 and No. 2 offshore converter stations via independent "offshore wind farm AC collection submarine cables." The No. 1 and No. 2 offshore converter stations have similar structures, each containing a "No. 1 2-pulse diode rectifier valve" as a passive converter valve and "No. 1 flexible DC converter valve" and "No. 2 flexible DC converter valve" as voltage source converter valves. The two offshore converter stations are connected via an "inter-station interconnection AC submarine cable" to achieve power sharing and backup. The DC sides of the two converter stations are connected in parallel via "positive DC transmission submarine cables" and "negative DC transmission submarine cables," respectively, and are connected to the No. 3 onshore converter station, ultimately connecting to the "receiving-end power grid." This specific architecture provides the physical basis for the system startup control and steady-state operation control methods described in steps S110 to S120 below. For example, in step S110, the voltage source converter valve (corresponding to "1# Flexible DC Converter Valve") and the passive converter valve (corresponding to "1# 2-pulse diode rectifier valve") in the first offshore converter station (corresponding to "1# Offshore Converter Station"), and the voltage source converter valve (corresponding to "2# Flexible DC Converter Valve") in the second offshore converter station (corresponding to "2# Offshore Converter Station") are controlled sequentially, which is based on this hardware connection. In step S120, the voltage source converter valves of the two offshore converter stations are controlled to operate in grid control mode and dynamic voltage control mode respectively, and coordinated using "inter-station interconnection AC submarine cable". This is also based on this topology, thereby effectively improving the reliability and economy of large-scale centralized offshore wind power transmission.

[0047] Next, according to the first aspect, the present invention provides a control method for an offshore wind power hybrid DC transmission system, which is based on the offshore wind power hybrid DC transmission system of the above embodiment. This system can integrate multiple offshore wind farms located in different sea areas, multiple offshore converter platforms configured with different converter valve combinations, and AC / DC submarine cable networks connecting these platforms to the land. Specifically, the system can gradually resume operation through a preset black-start process without external AC power support, completing the entire process from DC voltage establishment, offshore AC island grid construction to sequential grid connection of wind turbines. Based on the real-time power output of each offshore wind farm and the operating status of the converter station, it performs cross-station coordinated voltage and power control, smoothing out disturbances caused by wind power fluctuations and generating a stable and efficient offshore wind power DC power flow. Specifically, the hardware equipment of the system includes, but is not limited to: offshore wind turbines, AC collection submarine cables, inter-station interconnection AC submarine cables, 12-pulse diode rectifier valves (or passive converter valves), flexible DC converter valves (or voltage source converter valves, such as modular multilevel converter valves), inter-station interconnection DC submarine cables, positive / negative DC transmission submarine cables, onshore flexible DC converter stations, AC and DC side circuit breakers, voltage and current sensors, and control and communication networks (such as fiber optic communication networks) connecting each station.

[0048] like Figure 2 As shown, the method may include: Step S110: In response to the system startup command, the system startup control steps are executed sequentially by controlling the voltage source converter valves in the onshore converter station, the first offshore converter station, the offshore wind farm cluster, the passive converter valves in the first offshore converter station, and the voltage source converter valves in the second offshore converter station.

[0049] The purpose of this step is to sequentially power on and unlock the key nodes of the offshore wind power hybrid DC transmission system and establish energy through preset timing logic, thereby ensuring that the system remains stable during startup and avoiding voltage and current surges.

[0050] Specifically, the system can use the main controller to send unlocking commands and reference value commands containing specific target values ​​to the onshore converter station, the first offshore converter station, the offshore wind farm cluster, and the second offshore converter station in sequence according to the preset startup logic sequence, so as to establish DC voltage and AC voltage in sequence.

[0051] For example, the system can perform startup control according to the following specific parameters and procedures: First, unlock the onshore converter station and adjust its DC voltage setting value to 800kV; then, unlock the voltage source converter valve in the first offshore converter station, set its AC side voltage to 230kV, and set the frequency to 50.0 Hz; then, issue a grid connection command to the offshore wind farm cluster; next, unlock the passive converter valve in the first offshore converter station, which refers to a converter based on line commutation technology that does not have the ability to independently construct AC voltage; finally, unlock the voltage source converter valve in the second offshore converter station and set its AC voltage to 345kV.

[0052] In another embodiment, such as Figure 3 This diagram illustrates a flowchart of the startup control method for an offshore wind power hybrid DC transmission system according to a specific embodiment of the present invention. The flowchart specifically demonstrates the complete and orderly control logic sequence of the system from DC voltage establishment to grid connection and power transmission.

[0053] Figure 3 It includes five main steps executed sequentially, steps S1 to S5. Step S1 corresponds to controlling the onshore converter station to start up and operate in DC voltage control mode. Specifically, it involves starting the receiving-end onshore converter station, establishing the system DC voltage and increasing it to the rated voltage, for example, smoothly increasing the DC voltage from 0kV to... Step S2 corresponds to starting the voltage source converter valve (i.e., flexible DC converter valve) configured in the first offshore converter station (i.e., offshore converter station 1) and setting it to grid-connection control mode. Specifically, after the offshore converter station completes pre-charging, the flexible DC converter valve of offshore converter station 1 operates in V / f (voltage / frequency) grid-connection control mode, for example, controlling its AC bus voltage to 230kV and frequency to 50.0Hz. Step S3 corresponds to sending grid connection instructions to the offshore wind farm cluster. Specifically, the offshore wind turbines are connected to the grid sequentially, for example, at 2-second intervals, one wind farm or a group of wind turbines are connected to the stable AC grid in an orderly manner. Step S4 corresponds to engaging the passive converter valve (i.e., 12-pulse diode rectifier valve) in the first offshore converter station. Specifically, the 12-pulse diode rectifier valve of offshore converter station 1 is engaged, participating in system operation together with the flexible DC converter valve. For example, when the voltage across the rectifier valve is detected to meet the engagement conditions, its AC side circuit breaker is closed. Step S5 corresponds to setting the control mode of the voltage source converter valve in the second offshore converter station (i.e., offshore converter station 2) and completing the power transmission. Specifically, the control strategy of the flexible DC converter valve of offshore converter station 2 is set to dynamic voltage control mode, and the offshore wind power is sent to the DC transmission system and transmitted to the onshore power grid through the converter equipment. For example, the converter valve is set to a dynamic voltage support mode with a target voltage of 345kV.

[0054] This flowchart clearly details and visualizes the "system startup control steps" covered by step S110 in the aforementioned method embodiments, clarifies the execution order and technical points of each step, and provides clear operational guidance for those skilled in the art to implement the present invention.

[0055] Step S120: After the offshore wind power hybrid DC transmission system is started up and connected to the receiving end AC grid, the steady-state operation control steps are executed to control the voltage source converter valve in the first offshore converter station to operate in the grid-connected control mode, control the voltage source converter valve in the second offshore converter station to operate in the dynamic voltage control mode, and control the onshore converter station to operate in the DC voltage control mode.

[0056] This step aims to assign differentiated steady-state control objectives to the system to optimize the overall power transmission stability and AC voltage support capability. Grid control mode refers to a control strategy that establishes and maintains AC grid voltage and frequency reference values ​​by controlling the converter output; dynamic voltage control mode refers to a control strategy that maintains the AC voltage of a specified bus within a set range by rapidly adjusting the reactive power output of the converter; and DC voltage control mode refers to a control strategy that maintains a constant DC network voltage by adjusting the active power absorbed or generated by the converter.

[0057] Specifically, the system can achieve grid control by configuring an inner-loop current controller and an outer-loop power controller for the voltage source converter valve of the first offshore converter station; achieve dynamic voltage control by configuring a closed-loop controller with AC bus voltage as feedback for the voltage source converter valve of the second offshore converter station; and achieve DC voltage control by configuring a closed-loop controller with DC line voltage as feedback for the onshore converter station.

[0058] For example, the system can set the following control parameters during steady-state operation: In the grid control mode of the voltage source converter valve of the first offshore converter station, the voltage reference value is set to 1.0 per unit value ( The frequency reference value is set to 50.0Hz, and the proportional gain of the outer loop power controller is... Set to 1.5, integral coefficient The target value for AC voltage control is set to 0.1; in the dynamic voltage control mode of the voltage source converter valve of the second offshore converter station, the target value for AC voltage control is set to 1.02pu and the voltage-reactive power droop coefficient is set to 3.0%; in the DC voltage control mode of the onshore converter station, the target value for DC voltage control is set to 800kV.

[0059] In another embodiment, such as Figure 4This diagram illustrates a dynamic voltage control system block diagram of a voltage source converter valve (i.e., a modular multilevel converter valve) applied to a second offshore converter station, according to a specific embodiment of the present invention. The diagram specifically reveals the closed-loop implementation architecture that transforms the "dynamic voltage control mode" control strategy into specific control signals and execution actions.

[0060] Figure 4 The main body of the system demonstrates the complete signal chain from high-level control commands to low-level power device trigger pulses. The system is centered around a "dynamic voltage control module," which receives AC bus voltage reference values ​​from the system-level controller. (e.g., 345kV) and the actual measured value And calculate the reference value of reactive power required to maintain this voltage. Subsequently, the "PI controller" (proportional-integral controller) adjusts the reactive power reference value. With actual reactive power The deviation is calculated using proportional-integral operations, for example, the proportionality coefficient. Set to 1.2, integral coefficient Set to 0.08, output d-axis current reference value. This current reference value is compared with the measured current value from the "AC current control module," and a corresponding voltage modulation command is generated through the inner-loop current regulator (which typically also uses PI control). and The "circulating current control module" is responsible for suppressing the circulating current between the phase arms of the modular multilevel converter valve to ensure the equalization of the submodule capacitor voltage and system stability. The final voltage modulation command is processed by the "modulation strategy module" (e.g., nearest-level approximation modulation) and the "modulation signal module" to generate the switching status signal for each submodule. This signal is then converted into a specific "trigger pulse" by the "trigger logic module," driving hundreds of Insulated Gate Bipolar Transistors (IGBTs) in the converter valve to perform switching actions. This precisely controls the amplitude and phase of the AC voltage output by the converter valve, achieving dynamic and rapid adjustment of the AC bus voltage at the grid connection point. This control block diagram provides a specific and feasible implementation scheme for achieving the "controlling the voltage source converter valve in the second offshore converter station to operate in dynamic voltage control mode" described in step S120 of the aforementioned method embodiment.

[0061] In another embodiment, such as Figure 5 This diagram illustrates the principle block diagram of the Vf grid-connected control system for a voltage source converter valve (i.e., a modular multilevel converter valve) applied to a first offshore converter station, according to a specific embodiment of the present invention. The diagram specifically reveals the implementation architecture for translating the "grid-connected control mode" strategy into a concrete internal control signal flow.

[0062] Figure 5 The core of the system is the "Vf network control" module, which receives AC voltage reference values ​​from the system-level controller. (e.g., 230kV) and frequency reference value (e.g., 50.0Hz). Internally, this is calculated using a formula (e.g., the expression is...). This indicates that the active current reference component is generated from voltage and frequency reference values. The process involves calculations between the current sensor (the "PI controller") and the "PI controller" (proportional-integral controller) to generate a current reference signal for inner-loop control. Simultaneously, the "generate reference phase angle" module calculates the current reference signal based on the frequency reference value. Integral generation of the reference phase angle of the synchronous rotating coordinate system Subsequently, the "AC current control" module, based on the deviation between the current reference value and the actual feedback current, and in conjunction with... The reference component of the voltage modulation wave is calculated. The "circulating current control" module is used to suppress the internal circulating current between the phase arms of the converter valve. The processed modulation command passes through the "modulation strategy" module (e.g., nearest-level approximation modulation) and the "modulation signal" module, and finally the "trigger logic" module generates a specific "trigger pulse" to drive the switching action of the power semiconductor devices (such as IGBTs) of the converter valve, thereby accurately and autonomously establishing and maintaining the voltage amplitude and frequency of the AC bus. This block diagram illustrates the internal implementation process of "controlling the voltage source converter valve in the first offshore converter station to operate in the grid control mode" described in step S120 of the aforementioned method embodiment.

[0063] In another embodiment, such as Figure 6 This diagram illustrates a block diagram of a DC voltage and AC current coordinated control system applied to an onshore converter station, based on a specific embodiment of the present invention. The diagram specifically reveals the complete closed-loop control architecture that transforms the "DC voltage control mode" strategy into underlying current loop control commands, ultimately generating converter valve trigger pulses.

[0064] Figure 6 Starting with the "DC voltage control" module, this module receives DC voltage reference values. (e.g., 800kV) and actual DC voltage measurement value The feedback signal is processed by the "PI controller" (proportional-integral controller, labeled PI0 in the figure) to output the active power reference value required to maintain the DC voltage or directly convert it into the d-axis current reference component. Simultaneously, this module also receives reactive power reference values. Feedback to the actual reactive power Q is used to independently control the reactive power or AC voltage of the system, and to output the q-axis current reference component. Subsequently, the "AC current control" module uses the current reference value in the dq coordinate system. , And actual current feedback, quickly generate voltage commands , The "Generate Reference Phase Angle" module then uses the input grid voltage... The signal is used to generate the phase angle of a synchronous rotating coordinate system through algorithms such as phase-locked loops. This provides a reference for coordinate transformation. The "circulating current control" stage is used to suppress the unique arm circulating current of the modular multilevel converter valve and correct the voltage command. The corrected modulation signal enters the "modulation strategy" module (e.g., nearest-level approximation modulation), and finally the "trigger logic" generates a specific "trigger pulse" to drive the power devices (such as IGBTs) of the converter valve to operate, thereby achieving precise closed-loop control of DC voltage and rapid tracking of AC current. This block diagram is a specific implementation example at the controller level of "controlling the onshore converter station to operate in DC voltage control mode" in the aforementioned method embodiments, reflecting the core principle of the coordinated operation of the DC voltage outer loop and the AC current inner loop.

[0065] Therefore, according to the above implementation method, the system is first realized through the coordinated arrangement and connection of offshore wind farm clusters, offshore converter station clusters, inter-station interconnection networks (composed of AC submarine cables and DC submarine cables) and onshore converter stations. The system comprises an offshore converter station cluster, including at least one first offshore converter station and at least one second offshore converter station, serving as a power collection and conversion node for multiple offshore wind farms. An inter-station interconnection AC submarine cable is installed between the AC buses of the first and second offshore converter stations to establish synchronous communication between the AC systems of different offshore wind farms. The positive DC terminal of the second offshore converter station is connected to the negative DC terminal of the first offshore converter station via an inter-station interconnection DC submarine cable to construct a series boost structure on the DC side. The positive DC terminal of the first offshore converter station and the negative DC terminal of the second offshore converter station are connected to the DC side of the onshore converter station via a DC transmission submarine cable to achieve efficient long-distance transmission of boosted DC power. A passive converter valve and a voltage source converter valve are configured in parallel in the first offshore converter station, and a voltage source converter valve is configured in the second offshore converter station to meet the economic and active control requirements of different operating stages of the system.

[0066] In this embodiment, addressing the low utilization rate of existing power transmission channels in the background art, at least two offshore converter stations are connected in series on the DC side. This allows multiple offshore wind farms to share the same set of DC transmission cables and onshore converter stations, achieving power channel reuse and resolving the shortcomings of low asset utilization and poor engineering economy caused by constructing separate point-to-point DC channels for each wind farm. Addressing the lack of cross-wind farm power coordination and mutual assistance capabilities in existing technologies, this embodiment connects the offshore converter stations on the AC side using inter-station interconnection AC submarine cables and constructs a series-step-up electrical connection on the DC side. This provides a physical path for power interaction and redistribution between different wind farms, solving the problem of isolated wind farms and their transmission channels, which cannot provide power support in case of uneven output or failure. Therefore, the technical solution of this invention solves the technical problem of lacking cross-wind farm power coordination and mutual assistance capabilities in multi-wind farm grid connection scenarios, improving the overall operational economy and flexibility of the system.

[0067] In some embodiments, the steps of performing system startup control include: The onshore converter station is started and operated in DC voltage control mode to control the DC side output voltage of the onshore converter station to reach and maintain the first DC voltage reference value.

[0068] This step aims to first establish the base voltage of the DC network from the onshore converter station on the receiving end of the grid, so as to provide stable DC voltage support for the subsequent unlocking and grid connection of offshore converter stations and wind farm clusters.

[0069] Specifically, the main controller sends an unlock command containing a first DC voltage reference value to the onshore converter station. The onshore converter station's controller, based on a DC voltage control mode, adjusts the switching state of the converter bridge arms to bring the DC line voltage to the target value. For example, the first DC voltage reference value is set to 800kV. The onshore converter station's DC voltage controller uses proportional-integral control, with a proportional coefficient... Set to 2.0, integral coefficient Set to 0.05.

[0070] The voltage source converter valve configured in the first offshore converter station is started, and the control mode of the voltage source converter valve is set to the grid control mode, so as to control the AC side output voltage amplitude and frequency of the voltage source converter valve to reach and maintain the first AC voltage reference value and the first frequency reference value, respectively.

[0071] This step aims to establish a stable voltage and frequency reference in the offshore AC network by the voltage source converter valve of the first offshore converter station, so as to provide an AC grid that meets the grid connection conditions for the offshore wind farm cluster.

[0072] Specifically, after confirming that the DC voltage has stabilized at the first DC voltage reference value, the main controller sends an unlocking and mode setting command to the voltage source converter valve of the first offshore converter station. This converter valve generates a corresponding modulation signal based on the grid control mode algorithm to control its AC side output voltage. For example, the first AC voltage reference value is set to 230kV, and the first frequency reference value is set to 50.0Hz. The proportional gain of the outer loop voltage controller in the grid control is... Set to 1.2, integral coefficient Set to 0.15.

[0073] After monitoring that the AC side voltage and frequency have reached the first AC voltage reference value and the first frequency reference value and entered a stable state, grid connection commands are sent sequentially to each wind turbine in the offshore wind farm cluster.

[0074] The "grid connection command" refers to the command that closes the grid connection circuit breaker of the wind turbine to connect it to the AC power grid. "Stable state" refers to the state in which the measured values ​​of AC voltage and frequency remain within the allowable deviation range of their respective reference values. This step aims to orderly connect the wind farm cluster to the established stable AC network.

[0075] Specifically, the system monitors the voltage and frequency of the AC bus at the first offshore converter station. When the steady-state conditions are met, the main controller sends a grid connection command to the central controller or converter of each wind turbine. For example, the steady-state conditions can be set as follows: voltage between 229.5kV and 230.5kV, frequency between 49.98Hz and 50.02Hz, maintained for 5 seconds. The interval between sending the grid connection command can be set to 2 seconds.

[0076] The AC side circuit breaker connected to the passive converter valve in the first offshore converter station is closed to activate the passive converter valve.

[0077] This step aims to connect the passive converter valve to the AC system once the voltage conditions at both ends are met, allowing it to begin participating in power transmission.

[0078] Specifically, after an offshore wind farm cluster is connected to the grid and transmits a certain amount of power, and the AC voltage on the valve side of the passive converter valve is established, the main controller sends a closing command to the circuit breaker connecting the passive converter valve and the AC bus. For example, when the AC voltage on the valve side of the passive converter valve reaches 99% of the rated voltage and its DC voltage reaches 95% of the rated value, the main controller issues a circuit breaker closing command after a 1-second delay.

[0079] Set the control mode of the voltage source converter valve configured in the second offshore converter station to dynamic voltage control mode.

[0080] This step aims to configure the second offshore converter station as a dynamic voltage support point to enhance the voltage stability of another segment of the offshore AC network.

[0081] Specifically, after the second offshore converter valve is unlocked, the main controller sends a control mode command to it. The converter valve's controller switches to dynamic voltage control mode, using the connected AC bus voltage as the control target to adjust reactive power output. For example, the target voltage for dynamic voltage control mode is set to 345kV, i.e., the second AC voltage reference value. The voltage regulator proportional gain in this mode... Set to 3.0, integral coefficient Set to 0.2.

[0082] Therefore, according to the above implementation method, the system can ensure the smooth start-up of the offshore wind power hybrid DC transmission system through strict timing and mode coordination sequence control, avoid equipment overvoltage and start-up overcurrent, and gradually establish a stable power transmission channel.

[0083] In some embodiments, after performing the steady-state operation control step, the method further includes: Control the voltage source converter valve operating in the grid control mode so that the voltage amplitude and frequency of the AC bus of the first offshore converter station track the second AC voltage reference value and the second frequency reference value, respectively.

[0084] This step aims to finely adjust the voltage and frequency levels of the offshore AC network during the steady-state operation phase, based on grid dispatch instructions or optimized operational targets. The "second AC voltage reference value" and "second frequency reference value" are steady-state operation target values ​​that differ from the values ​​set during the startup phase.

[0085] Specifically, the main controller or energy management system sends updated voltage and frequency setpoint commands to the voltage source converter valve of the first offshore converter station operating in grid-connected control mode. The outer loop of the grid-connected control of this converter valve adjusts the setpoint of its internal controller according to the new reference values, thereby changing the amplitude and frequency of the AC output voltage. For example, upon receiving a dispatch command, the second AC voltage reference value is set to 228kV, and the second frequency reference value is set to 50.05Hz. The outer loop voltage controller of the grid-connected control will adjust according to the new reference values, and its control deviation is calculated as follows: .

[0086] The voltage source converter valve operating in dynamic voltage control mode is controlled. Based on the actual output power of the voltage source converter valve configured in the second offshore converter station and the operating parameters of the first offshore converter station, the DC voltage reference value of the voltage source converter valve configured in the second offshore converter station is calculated and tracked.

[0087] This step aims to achieve coordinated control of DC voltage between the two offshore converter stations, optimize power distribution, and improve system stability. "Actual output power" refers to the measured value of active power transmitted by the voltage source converter valve in the second offshore converter station, and "operating parameters" include the DC voltage and DC current of the first offshore converter station.

[0088] Specifically, the control system collects the active power of the second offshore converter valve in real time. DC voltage with the first offshore converter station DC current Based on power balance and resistance characteristics, calculate the DC voltage reference value for the second offshore converter valve. This value is then sent to the internal control loop of the converter valve. For example, consider the resistance of a DC submarine cable. 2.0 ohms ( The DC voltage reference value can be calculated using the following formula: Assuming the measurement is... It is 798kV. If it is 200MW, then the calculation is as follows This value will be sent as the target value to the DC voltage controller of the converter valve.

[0089] The onshore converter station, operating in DC voltage control mode, adjusts the DC-side voltage of the onshore converter station based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable.

[0090] This step aims to compensate for the voltage drop of the DC line by adjusting the DC voltage at the receiving-end converter station and adapting to changes in the total wind power, thereby maintaining the stability and efficiency of power transmission in the entire DC system. "Total output power" refers to the total active power transmitted from the offshore wind farm cluster to the DC system.

[0091] Specifically, the control system collects the DC current from the DC transmission submarine cable. and total output power The DC voltage controller of the onshore converter station, based on a preset regulation law, adds a compensation amount related to the line voltage drop to the rated DC voltage reference value to generate the final DC voltage control target value. .

[0092] For example, the equivalent resistance of a preset DC line 5.0Ω, rated DC voltage The voltage is 800kV. The adjustment formula can be: .like If it is 800MW, then the calculation is as follows The onshore converter station will track this target value and adjust accordingly.

[0093] Therefore, according to the above implementation method, the system can achieve multi-level, adaptive coordinated control in steady-state operation, optimize the system operating point, and improve the robustness and economy of offshore wind power transmission.

[0094] In some embodiments, the step of calculating and tracking the DC voltage reference value of the voltage source converter valve configured in the second offshore converter station based on the actual output power of the voltage source converter valve configured in the second offshore converter station and the operating parameters of the first offshore converter station includes: Obtain the rated DC voltage and the total actual output power of the first offshore converter station.

[0095] This step aims to obtain the basic operating parameters required for the calculation. "Rated DC voltage" refers to the design operating voltage value of the DC side of the first offshore converter station. "Total actual output power" refers to the measured value of the total active power delivered to the DC line through the first offshore converter station (including its voltage source converter valves and passive converter valves).

[0096] Specifically, the control system reads the rated DC voltage setpoint and the total output power value calculated in real time from the DC voltage transformers and DC current transformers of the first offshore converter station, or from data uploaded by the converter station controller. For example, the rated DC voltage of the first offshore converter station is obtained from the system database or the controller. The total actual output power of the first offshore converter station was obtained through real-time data acquisition. .

[0097] The proportional coefficient is determined based on the rated DC voltage of the first offshore converter station and the total actual output power of the first offshore converter station.

[0098] This step aims to calculate a proportionality coefficient K to characterize the equivalent resistance of the DC line, based on the operating conditions of the first offshore converter station. The "proportionality coefficient K" is a coefficient used to map power values ​​to changes in DC voltage, and its physical meaning is related to the equivalent resistance of the DC circuit.

[0099] Specifically, the proportionality coefficient K is calculated by dividing the total actual output power of the first offshore converter station by the square of its rated DC voltage, and then multiplying by a preset line resistance coefficient C. The formula is: The coefficient C is a preset constant related to the resistance of the DC submarine cable, with units of... For example, the preset line resistivity C = 2.5. Substitute the values ​​from the above example into the formula to calculate: The proportionality coefficient K is dimensionless and is used for subsequent calculations.

[0100] Based on the proportional coefficient and the actual output power of the voltage source converter valve configured in the second offshore converter station, the DC voltage reference value of the voltage source converter valve configured in the second offshore converter station is calculated.

[0101] This step aims to dynamically determine the DC voltage control target value of the converter valve based on the calculated proportional coefficient and the power borne by the second offshore converter valve, so as to achieve automatic coordination of power distribution.

[0102] Specifically, the actual output power of the voltage source converter valve in the second offshore converter station Multiply by the proportionality coefficient K, and then multiply the product by the rated DC voltage of the first offshore converter station. Add them together to obtain the DC voltage reference value. The formula is: For example, let the actual output power of the voltage source converter valve in the second offshore converter station be... Substitute the values ​​into the formula to calculate: The calculated value of 800.47kV will be used as the control target and sent to the voltage source converter valve of the second offshore converter station.

[0103] Therefore, according to the above implementation method, the system can automatically and dynamically calculate a DC voltage reference value that matches the power undertaken by the second offshore converter station based on the total power output of the first offshore converter station, thereby realizing coordinated control of the DC voltage between the two offshore converter stations and optimizing the system operating point.

[0104] In some embodiments, the step of adjusting the DC-side voltage of the onshore converter station based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable includes: The system acquires the DC current flowing through the DC transmission cable in real time and collects the output power of each offshore wind farm in the offshore wind power hybrid DC transmission system.

[0105] This step aims to provide real-time, accurate input data for optimized DC voltage regulation. "Real-time acquisition" refers to continuously measuring and reading data at set intervals. "Acquisition" refers to requesting or receiving power data from each wind farm control system.

[0106] Specifically, DC current values ​​are measured at fixed sampling periods using DC current transformers installed on the DC transmission submarine cable, and then uploaded to the main controller via a communication system. Simultaneously, the main controller periodically obtains the total active power values ​​of each offshore wind farm from its energy management platform or turbine group control system via a scheduling data network or dedicated communication channel. For example, the sampling frequency of the DC current transformer is set to 10 kHz, and the main controller reads the average current value every 100 milliseconds (ms). The main controller samples the output power from the three connected offshore wind farms every 200ms, which are respectively .

[0107] Based on the collected output power of each offshore wind farm, the total output power of the offshore wind power hybrid DC transmission system is calculated.

[0108] This step aims to aggregate the dispersed wind power data to obtain the total power output of the system, which serves as one of the core bases for voltage regulation. "Total output power" refers to the sum of the active power transmitted from all offshore wind farms to the DC system at the same time.

[0109] Specifically, within each calculation cycle, the main controller algebraically sums the output power values ​​of each wind farm collected at the same time segment or in the most recent cycle to obtain the total output power of the system. For example, at a certain calculation moment, the power of the three wind farms collected were respectively , , Then the total output power is calculated. This calculation is performed every 200ms.

[0110] Based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable, the reference value of the DC side voltage of the onshore converter station is calculated.

[0111] This step aims to dynamically calculate the optimal DC voltage control target value for the onshore converter station based on real-time operating conditions, thereby optimizing system operating efficiency and stability. The "DC side voltage reference value" is the target setpoint for the DC voltage controller of the onshore converter station.

[0112] Specifically, the control system will control the total output power. and DC current Substituting the values ​​into the preset voltage-power-current coordination calculation formula, the DC side voltage reference value is calculated. This formula typically includes a reference value for the rated DC voltage. And the adjustment amount determined by the total output power and DC current. One implementation of the formula is as follows: .in, This is the power regulation coefficient, in units of... ; This is the current regulation coefficient, in units of... For example, setting the rated DC voltage reference value. Power regulation coefficient Current regulation coefficient If currently , Then calculate DC side voltage reference value: .

[0113] Control the onshore converter station to ensure that the DC-side voltage of the onshore converter station tracks the DC-side voltage reference value.

[0114] This step aims to transform the calculated theoretical optimal voltage reference value into the actual control action of the onshore converter station, completing closed-loop regulation. "Tracking" refers to using closed-loop control to make the controlled variable (measured DC voltage) approach the target variable (DC-side voltage reference value).

[0115] Specifically, the main controller will calculate the The DC voltage control loop is sent to the onshore converter station. This control loop uses proportional-integral control (PIC). Based on the deviation between the voltage reference value and the measured value, it calculates and outputs control signals for the modulation stage, thereby adjusting the switching state of the converter bridge arms and ultimately changing the DC-side voltage. For example, the DC voltage controller of the onshore converter station receives... The controller will collect the current measured DC voltage value upon receiving the instruction. Calculate the deviation The deviation signal passes through a proportional-integral controller (e.g., the proportional coefficient). Integral coefficient The system performs calculations to generate control signals, which drive the converter to adjust the DC voltage to 802.86kV.

[0116] Therefore, according to the above implementation method, the system can dynamically and adaptively calculate and set the optimal DC voltage of the onshore converter station based on the changes in the total wind power and line current, thereby realizing the coordinated optimization control of active power and voltage of the DC transmission system, reducing line losses and improving system stability.

[0117] In some embodiments, a reference value for the DC-side voltage of the onshore converter station is calculated based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable, including: Divide the total output power of the offshore wind power hybrid DC transmission system by the DC current of the DC transmission submarine cable to obtain the reference value of the DC side voltage of the onshore converter station.

[0118] This calculation step is directly based on the fundamental physical relationship of DC power transmission, namely, DC power equals the product of DC voltage and DC current. Through this calculation, the obtained DC-side voltage reference value can theoretically be perfectly adapted to real-time power and current, thus providing a theoretically ideal DC voltage setpoint at the onshore converter station for optimizing system operation.

[0119] Specifically, the control system will calculate the total output power of the system in real time. The DC transmission cable current obtained by real-time measurement Substitute into the formula The reference value of the DC side voltage of the onshore converter station can be directly calculated. This method requires no preset line resistance parameters; it directly utilizes real-time measured electrical quantities for calculation. For example, within one control cycle, the system calculates the total output power of the offshore wind power hybrid DC transmission system. It is 600MW, that is Meanwhile, the DC transmission cable current measured by the DC current transformer... The current rating is 1.2kA, or 1200A. The reference value for the DC-side voltage is calculated using the formula: The calculated 500kV will be used as the target reference value for the DC voltage controller of the onshore converter station during the current control cycle.

[0120] Therefore, according to the above implementation method, the system can directly and quickly calculate the DC voltage reference value of the onshore converter station that matches the current transmission power based on real-time power and current measurements, providing an adaptive dynamic target for DC voltage control and helping to achieve automatic optimization of the system operating point.

[0121] In some embodiments, since the first offshore converter station and the second offshore converter station are connected in series on the DC side, the DC current flowing through them is the same. In order to achieve coordinated power transmission and optimize the system operating point, this embodiment proposes a DC voltage coordination control strategy based on power adaptation. The core idea is to make the DC voltage borne by each offshore converter station proportional to the active power transmitted to the DC line. Based on this, the DC voltage reference value of the voltage source converter valve in the second offshore converter station (offshore converter station 2) can be calculated by the following formula (1): (1) Formula (1) is called the DC voltage reference value calculation formula based on power adaptation, which is used to dynamically set the DC voltage control target based on the real-time power output of the offshore converter station 2. This represents the DC voltage reference value for offshore converter station 2 to be calculated. The subscript "dc" indicates DC, and "ref" indicates reference value. The unit is usually 1. . This indicates the actual output power of offshore converter station 2, which is the measured value of the active power transmitted from the converter station to the DC line, usually in MW. This indicates the rated DC voltage of the first offshore converter station (offshore converter station 1), which is the design operating voltage value of its DC side, usually in kV. This represents the actual output power of the first offshore converter station (offshore converter station 1), that is, the measured total active power flowing through the passive converter valves and voltage source converter valves of this station, usually in MW. The proportional gain k is an adaptation coefficient that converts a power value to a voltage value. Its physical meaning is the DC voltage regulation corresponding to a unit power change under the current operating conditions of the system, and its value is... .

[0122] Next, in this embodiment, the system can also calculate the DC voltage control reference value of the onshore converter station (onshore converter station 3) using formula (2): (2) Formula (2) is called the direct calculation formula for DC voltage with power-current ratio. It is used to directly determine the DC voltage setting value required for the onshore converter station to maintain power balance based on the total power and DC current transmitted by the system in real time. This represents the reference value of the DC voltage of the onshore converter station to be calculated, in kV. This represents the total output power of the offshore wind farm, which is the sum of the active power transmitted from all offshore wind farms to the DC system through various offshore converter stations. The unit is typically MW. This data is collected by the power detection devices at each offshore converter station and transmitted to the onshore station via an inter-station fiber optic communication network. In this system, the communication delay is strictly controlled to within 3 microseconds. Within a certain range to ensure data timeliness. This represents the system's DC current, specifically the measured total DC current flowing through critical circuits such as the DC transmission submarine cable, typically measured in kiloamperes (kA). This current value is directly detected in real time using DC current sensors installed on the critical circuits, with no data transmission delay.

[0123] Therefore, by combining the above formulas (1) and (2), the system can achieve coordinated hierarchical voltage control of the offshore wind power hybrid DC transmission system. Formula (1) ensures the power distribution and DC voltage coordination among different offshore converter stations, while formula (2) ensures that the onshore converter station can quickly and accurately adapt to changes in the total power and current of the system, maintain the voltage stability and power balance of the entire DC network, thereby improving the system's operational stability and flexibility under complex operating conditions.

[0124] In some embodiments, the passive converter valve of the offshore wind power hybrid DC transmission system is a multi-pulse diode rectifier valve, and the voltage source converter valve is a modular multilevel converter valve.

[0125] Among them, the multi-pulse diode rectifier valve refers to a converter device composed of multiple phase-shifting transformers and diode rectifier bridges, which can achieve high pulse number uncontrolled rectification. It does not have active turn-off capability and relies on the AC system voltage to achieve commutation. The modular multilevel converter valve refers to a voltage source converter composed of a large number of structurally identical sub-modules cascaded together. It can directly output high-quality multilevel waveforms by controlling the switching on and off of sub-modules.

[0126] Specifically, the multi-pulse diode rectifier valve generates multiple sets of AC voltages with a certain phase difference through a phase-shifting transformer, supplying multiple three-phase diode rectifier bridges. The outputs of each rectifier bridge are connected in series or parallel on the DC side, thereby synthesizing a high-pulse DC voltage on the DC side, effectively reducing harmonic content. The modular multilevel converter valve determines whether a submodule outputs voltage by controlling the switching state of fully controllable devices (such as IGBTs) in each submodule. Through the superposition of the output voltages of multiple submodules, a near-sinusoidal stepped wave voltage is synthesized at the converter valve output. For example, a passive converter valve can use four phase-shifting transformers (with phase shift angles of...) A 36-pulse diode rectifier valve, consisting of a rectifier circuit and four three-phase full-bridge rectifier circuits, has a rated DC-side voltage of [voltage value missing]. The rated power is 1200MW. The voltage source converter valve can be a modular multilevel converter valve composed of half-bridge sub-modules. Each converter valve arm is composed of 200 sub-modules cascaded together. The rated voltage of the DC capacitor of a single sub-module is 2kV and the capacitance value is 6 millifarads (mF). The rated capacity of a single converter station is 900 megavolt-amperes (MVA).

[0127] Therefore, by utilizing the aforementioned offshore wind power hybrid DC transmission system, users can realize a hybrid DC transmission architecture that combines the high reliability and low cost advantages of multi-pulse diode rectifier valves in high-voltage, high-capacity transmission with the flexible control advantages of modular multilevel converter valves in reactive power support, fault ride-through, and black start, thereby improving the overall economy and operational reliability of the offshore wind power transmission system.

[0128] The specific functions and examples of each module and submodule of the device in this embodiment of the invention can be found in the relevant descriptions of the corresponding steps in the above method embodiments, and will not be repeated here.

[0129] According to a fourth aspect, the present invention provides an electronic device comprising: At least one processor; and a memory communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor, which are executed by the at least one processor to enable the at least one processor to execute any of the offshore wind power hybrid DC transmission system control methods in the embodiments of the present invention.

[0130] According to another aspect of the present invention, a non-transitory computer-readable storage medium storing computer instructions is provided, wherein the computer instructions are used to cause a computer to execute any of the offshore wind power hybrid DC transmission system control methods in the embodiments of the present invention.

[0131] Figure 7 A schematic block diagram of an example electronic device 600 that can be used to implement embodiments of the present invention is shown. The electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device may also represent various forms of mobile devices, such as personal digital assistants, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely illustrative and are not intended to limit the implementation of the invention described and / or claimed herein.

[0132] like Figure 7 As shown, the electronic device 600 includes a computing unit 601, which can perform various appropriate actions and processes based on a computer program stored in a read-only memory (ROM) 602 or a computer program loaded from a storage unit 608 into a random access memory (RAM) 603. The RAM 603 may also store various programs and data required for the operation of the electronic device 600. The computing unit 601, ROM 602, and RAM 603 are interconnected via a bus 604. An input / output (I / O) interface 605 is also connected to the bus 604.

[0133] Multiple components in electronic device 600 are connected to I / O interface 605, including: input unit 606, such as keyboard, mouse, etc.; output unit 607, such as various types of displays, speakers, etc.; storage unit 608, such as disk, optical disk, etc.; and communication unit 609, such as network card, modem, wireless transceiver, etc. Communication unit 609 allows electronic device 600 to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0134] The computing unit 601 can be various general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the computing unit 601 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various special-purpose artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, a digital signal processor (DSP), and any suitable processor, controller, microcontroller, etc. The computing unit 601 performs the various methods and processes described above, such as a control method for an offshore wind power hybrid DC transmission system. For example, in some embodiments, a control method for an offshore wind power hybrid DC transmission system can be implemented as a computer software program tangibly contained in a machine-readable medium, such as storage unit 608. In some embodiments, part or all of the computer program can be loaded and / or installed on the electronic device 600 via ROM 602 and / or communication unit 609. When the computer program is loaded into RAM 603 and executed by the computing unit 601, one or more steps of the control method for an offshore wind power hybrid DC transmission system described above can be performed. Alternatively, in other embodiments, the computing unit 601 may be configured by any other suitable means (e.g., by means of firmware) to perform a control method for an offshore wind power hybrid DC transmission system.

[0135] Various embodiments of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SoCs), payload-programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include implementations in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a dedicated or general-purpose programmable processor, capable of receiving data and instructions from a storage system, at least one input device, and at least one output device, and transmitting data and instructions to the storage system, the at least one input device, and the at least one output device.

[0136] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0137] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0138] To provide interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device (e.g., a CRT or LCD monitor) for displaying information to the user; and a keyboard and pointing device (e.g., a mouse or trackball) through which the user provides input to the computer. Other types of devices can also be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual, auditory, or tactile feedback); and input from the user can be received in any form (including sound input, voice input, or tactile input).

[0139] The systems and technologies described herein can be implemented in computing systems that include back-end components (e.g., as a data server), or computing systems that include middleware components (e.g., an application server), or computing systems that include front-end components (e.g., a user computer with a graphical user interface or web browser through which a user can interact with implementations of the systems and technologies described herein), or any combination of such back-end, middleware, or front-end components. The components of the system can be interconnected via digital data communication of any form or medium (e.g., a communication network). Examples of communication networks include local area networks (LANs), wide area networks (WANs), and the Internet.

[0140] Computer systems can include clients and servers. Clients and servers are generally located far apart and typically interact via communication networks. Client-server relationships are created by computer programs running on the respective computers and having a client-server relationship with each other. Servers can be cloud servers, servers in distributed systems, or servers incorporating blockchain technology.

[0141] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0142] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the principles of this invention should be included within the scope of protection of this invention.

Claims

1. A hybrid DC transmission system for offshore wind power, characterized in that, It includes offshore wind farm clusters, offshore converter station clusters, inter-station interconnection AC submarine cables, inter-station interconnection DC submarine cables, DC transmission submarine cables, and onshore converter stations; The offshore wind farm cluster is connected to the offshore converter station cluster via an AC convergence submarine cable. The offshore converter station cluster includes at least one first offshore converter station and at least one second offshore converter station; The AC busbars of the first offshore converter station and the second offshore converter station are electrically connected via the inter-station interconnection AC submarine cable; The positive DC-side terminal of the second offshore converter station is connected to the negative DC-side terminal of the first offshore converter station via the inter-station interconnection DC submarine cable, forming a series boost structure on the DC side; The DC transmission submarine cable includes a positive DC transmission submarine cable and a negative DC transmission submarine cable. The positive DC side of the first offshore converter station is connected to the positive DC transmission submarine cable, and the negative DC side of the second offshore converter station is connected to the negative DC transmission submarine cable. The far ends of the positive DC transmission submarine cable and the negative DC transmission submarine cable are connected to the DC side of the onshore converter station. The AC side of the onshore converter station is used to connect to the receiving-end AC power grid; The first offshore converter station is equipped with a passive converter valve and a voltage source converter valve connected in parallel, and the second offshore converter station is equipped with the voltage source converter valve.

2. A control method for an offshore wind power hybrid DC transmission system, characterized in that, The method is based on the offshore wind power hybrid DC transmission system as described in claim 1, and includes: In response to the system startup command, the system sequentially controls the voltage source converter valves in the onshore converter station, the first offshore converter station, the offshore wind farm cluster, the passive converter valves in the first offshore converter station, and the voltage source converter valves in the second offshore converter station to execute the system startup control steps. After the offshore wind power hybrid DC transmission system is started and connected to the receiving-end AC grid, the steady-state operation control steps are executed to control the voltage source converter valve in the first offshore converter station to operate in the grid control mode, control the voltage source converter valve in the second offshore converter station to operate in the dynamic voltage control mode, and control the onshore converter station to operate in the DC voltage control mode.

3. The method according to claim 2, characterized in that, The steps for performing the system startup control include: The onshore converter station is controlled to start and operate in DC voltage control mode in order to control the DC side output voltage of the onshore converter station to reach and maintain the first DC voltage reference value; The voltage source converter valve configured in the first offshore converter station is started, and the control mode of the voltage source converter valve is set to the grid control mode, so as to control the AC side output voltage amplitude and frequency of the voltage source converter valve to reach and maintain the first AC voltage reference value and the first frequency reference value respectively. After monitoring that the AC side voltage and frequency have reached the first AC voltage reference value and the first frequency reference value and entered a stable state, grid connection commands are sent sequentially to each wind turbine in the offshore wind farm cluster. The AC side circuit breaker connected to the passive converter valve in the first offshore converter station is closed to engage the passive converter valve. Set the control mode of the voltage source converter valve configured in the second offshore converter station to dynamic voltage control mode.

4. The method according to claim 2, characterized in that, After performing the steady-state operation control step, the method further includes: The voltage source converter valve operating in the network control mode is controlled so that the voltage amplitude and frequency of the AC bus of the first offshore converter station track the second AC voltage reference value and the second frequency reference value, respectively. The voltage source converter valve operating in the dynamic voltage control mode is controlled. Based on the actual output power of the voltage source converter valve configured in the second offshore converter station and the operating parameters of the first offshore converter station, the DC voltage reference value of the voltage source converter valve configured in the second offshore converter station is calculated and tracked. The onshore converter station, operating in DC voltage control mode, adjusts the DC-side voltage of the onshore converter station based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable.

5. The method according to claim 4, characterized in that, The step of calculating and tracking the DC voltage reference value of the voltage source converter valve configured in the second offshore converter station based on the actual output power of the voltage source converter valve configured in the second offshore converter station and the operating parameters of the first offshore converter station includes: Obtain the rated DC voltage of the first offshore converter station and the total actual output power of the first offshore converter station; The proportionality coefficient is determined based on the rated DC voltage of the first offshore converter station and the total actual output power of the first offshore converter station. Based on the proportional coefficient and the actual output power of the voltage source converter valve configured in the second offshore converter station, the DC voltage reference value of the voltage source converter valve configured in the second offshore converter station is calculated.

6. The method according to claim 4, characterized in that, The step of adjusting the DC-side voltage of the onshore converter station based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable includes: The DC current flowing through the DC transmission submarine cable is acquired in real time, and the output power of each offshore wind farm in the offshore wind power hybrid DC transmission system is collected. Based on the collected output power of each offshore wind farm, the total output power of the offshore wind power hybrid DC transmission system is calculated. Based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable, the reference value of the DC side voltage of the onshore converter station is calculated. The onshore converter station is controlled to make its DC-side voltage track the DC-side voltage reference value.

7. The method according to claim 6, characterized in that, The calculation of the DC-side voltage reference value of the onshore converter station based on the total output power of the offshore wind power hybrid DC transmission system and the DC current of the DC transmission submarine cable includes: The reference value of the DC side voltage of the onshore converter station is obtained by dividing the total output power of the offshore wind power hybrid DC transmission system by the DC current of the DC transmission submarine cable.

8. The offshore wind power hybrid DC transmission system according to claim 1, characterized in that, The passive converter valve is a multi-pulse diode rectifier valve, and the voltage source converter valve is a modular multilevel converter valve.

9. An electronic device, characterized in that, include: At least one processor; and a memory that is communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the method of any one of claims 2-7.

10. A non-transitory computer-readable storage medium storing computer instructions, characterized in that, in, Computer instructions are used to cause a computer to perform the method according to any one of claims 2-7.

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