COSCO ocean energy low frequency collection and transmission topology and control method thereof

Abstract

The COSCO Shipping New Energy low-frequency collection and transmission topology and its control method include connecting the output end of the offshore wind farm to an offshore low-frequency collection bus. The offshore low-frequency collection bus collects the low-frequency AC power from each offshore wind farm and transmits it to an onshore low-frequency collection bus via a single low-frequency submarine cable. All parallel transmission circuits are connected in parallel to the onshore low-frequency collection bus. The onshore low-frequency collection bus receives the low-frequency AC power transmitted from the low-frequency submarine cable and distributes the power to each parallel transmission circuit. The parallel transmission circuits include energy routers, power conversion devices, and / or transformers. The energy routers perform power flow control. This invention improves the operational reliability, equipment utilization, and engineering feasibility of the offshore wind power system.

Description

Technical Field

[0001] This invention belongs to the field of offshore wind power collection and transmission technology, and more specifically, relates to the low-frequency collection and transmission topology of offshore new energy and its control method. Background Technology

[0002] Existing offshore wind power aggregation and transmission solutions mainly include two technical routes: power frequency AC transmission and high-voltage flexible DC transmission. For power frequency AC transmission, as the length of the submarine cable increases, the cable charging current and reactive power demand rise significantly, leading to difficulties in voltage control, a decrease in effective transmission capacity, and the need for large-scale reactive power compensation devices, increasing engineering complexity and investment costs. In long-distance, large-capacity scenarios, the technical and economic feasibility and scalability of power frequency AC transmission are limited, making it difficult to support the rolling development and large-scale aggregation of offshore wind power from nearshore to mid-sea and offshore areas. To meet the needs of longer distances and larger-scale transmission, high-voltage flexible DC has been extensively researched and applied in the offshore wind power field. However, its core relies on high-power power electronic converters and complex control and protection systems: the short-term overload capacity of power electronic devices is relatively limited, and thermal and current margin constraints are obvious; under disturbances such as grid faults, converter station faults, or submarine cable faults, highly coordinated control and protection strategies are required to achieve fault ride-through and recovery; at the same time, the system structure is complex, the number of devices is large, and the construction and operation and maintenance costs of offshore converter stations are high, posing challenges to system reliability and economy.

[0003] As offshore wind power development shifts from single-farm scale to multi-cluster, large-scale operations, the collection and transmission patterns are gradually evolving from "point-to-point transmission from a single farm" to a systematic structure of "centralized collection and parallel transmission." Multiple offshore wind farms complete centralized collection on the seaside, then transmit power via submarine cables to shore-side collection nodes, and finally supply power to the grid or users through multiple parallel transmission circuits. This increases the scale of collection, enhances transmission flexibility, and adapts to phased construction needs. On the other hand, to reduce the impact of charging current on long-distance AC submarine cables, improve effective transmission capacity, and consider engineering economics, low-frequency AC transmission has gained attention as an alternative technology.

[0004] However, several key technical issues remain to be addressed in the aforementioned structure of "centralized collection on the sea side + low-frequency power transmission via submarine cables + parallel transmission from the shore side": First, the differences in landing points, laying paths, and lengths of multiple submarine cables lead to variations in distribution parameters. Coupled with fluctuations in wind power output and changes in operating modes, this can easily cause uneven power flow distribution and insufficient overload margin among the multiple submarine cables, reducing system capacity utilization. Second, in long-distance, high-capacity scenarios in the open ocean, insufficient support capacity of the low-frequency side collection bus may exacerbate the risk of voltage and frequency fluctuations. During fault disturbances, it is more likely to trigger wind turbine disconnection and a sharp drop in transmission capacity, thus placing higher demands on the low-frequency bus voltage and frequency support, controllable power flow distribution, and the redundancy and fault ride-through mechanisms of the parallel system. Therefore, a suitable offshore wind power collection and transmission scheme for the open ocean with coordinated power flow control and fault ride-through capabilities is urgently needed. Summary of the Invention

[0005] To address the problems of high reactive power demand, limited effective transmission capacity, and difficulty in system expansion in long-distance, large-capacity offshore wind power AC transmission, as well as the shortcomings of flexible DC transmission systems such as complex structure, high construction and operation costs of offshore converter stations, limited short-term overload margin, and complex fault ride-through control and protection, this invention provides a low-frequency collection and transmission topology for COSCO-COSCO offshore new energy and its control method.

[0006] The present invention adopts the following technical solution.

[0007] The first aspect of this invention proposes a low-frequency collection and transmission topology for COSCO Shipping New Energy, comprising: an offshore low-frequency collection bus, a low-frequency transmission submarine cable, an onshore low-frequency collection bus, and multiple parallel transmission circuits, specifically: The output end of COSCO Shipping's offshore wind farm is connected to the offshore low-frequency collection bus. The offshore low-frequency collection bus collects the low-frequency AC power of each connected offshore wind farm and transmits it to the onshore low-frequency collection bus through a low-frequency transmission submarine cable. The onshore low-frequency collection bus is connected to the power grid or users through several parallel outgoing circuits. The onshore low-frequency collection bus is used to receive the low-frequency AC power transmitted from the low-frequency submarine cable and then distribute the power to each parallel outgoing circuit. The parallel outgoing circuit is composed of an energy router and a power conversion device or an energy router, a power conversion device and a transformer. If there is no transformer, the energy router is used as the preceding circuit. Otherwise, the energy router and the transformer are connected in different ways to form the preceding circuit. The onshore low-frequency collecting bus is connected to one side of the power conversion device through a preceding circuit, and the other side of the power conversion device is connected to the power grid or user. The power conversion device is an AC converter. The low-frequency transmission submarine cable, the onshore low-frequency collecting bus, and all parallel transmission circuits together form a combined transmission module.

[0008] Preferably, the energy router and the transformer form a preceding circuit through different connection methods, specifically: The energy router can be connected in series or in parallel. When connected in series, the energy router, transformer, and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user, or the transformer, energy router, and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user. When connected in parallel, the transformer and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user, and the energy router is connected between the high-voltage side or low-voltage side of the transformer and the system reference point.

[0009] Preferably, the power conversion device in the parallel output circuit is an AC converter that converts low-frequency AC power into power-frequency AC power. The AC converter includes: an MG generator unit, a modular multilevel matrix converter (M3C), and any combination thereof. When the AC converter is an MG generator unit, the MG generator unit includes a motor and a generator, which are coaxially connected and perform electromechanical energy transfer. The motor side of the MG generator unit is electrically connected to the onshore low-frequency collecting bus, and the generator side of the MG generator unit outputs power-frequency AC power and is electrically connected to the power grid or the user side. The motor and / or generator is any combination of synchronous motors or asynchronous motors.

[0010] Preferably, when the wind power capacity connected to the offshore low-frequency collection bus exceeds the transmission capacity limit of a single-circuit low-frequency transmission submarine cable, the capacity of the COSCO Shipping New Energy low-frequency collection and transmission topology is expanded by adding a combined transmission module or a flexible DC extension module between the offshore low-frequency collection bus and the power grid or user.

[0011] Preferably, the capacity of the COSCO-COSCO offshore new energy low-frequency collection and transmission topology is expanded by adding a combined transmission module between the offshore low-frequency collection bus and the power grid or user, specifically as follows: Several combined transmission modules are added, and all combined transmission modules are connected in parallel between the offshore low-frequency collection bus and the power grid or user. The total number of combined transmission modules after the addition is greater than or equal to the wind power capacity connected to the offshore low-frequency collection bus divided by the transmission capacity limit of a single low-frequency submarine cable.

[0012] Preferably, the capacity of the COSCO-COSCO-Shanghai new energy low-frequency collection and transmission topology is expanded by adding a flexible DC extension module between the offshore low-frequency collection bus and the power grid or user, specifically as follows: The offshore low-frequency collection bus is connected to the power grid or users by connecting at least one flexible DC transmission branch. The flexible DC transmission branch consists of an offshore converter, a DC transmission submarine cable, and an onshore converter. The offshore low-frequency collection bus is connected to the input end of the offshore converter. The offshore converter and the onshore converter are connected by a DC transmission submarine cable. The output end of the onshore converter is connected to the power grid or users.

[0013] Preferably, the number of offshore low-frequency collection buses is set to one or more. The offshore low-frequency collection buses are set on the offshore collection platform. When a new offshore wind farm is added, a new offshore low-frequency collection bus is selected and the new offshore wind farm is connected to the new offshore low-frequency collection bus, or the new offshore wind farm is connected to the existing offshore low-frequency collection bus, and the number of access ports and collection capacity of the corresponding offshore low-frequency collection bus are expanded. When a new offshore wind farm is added, the corresponding offshore collection platform is expanded simultaneously.

[0014] Preferably, a bus tie switch is installed between different return low-frequency gathering buses at sea and between different return low-frequency gathering buses at shore. The bus tie switch is used to selectively connect or separate two corresponding connected buses to perform power mutual assistance, operation mode reconfiguration or maintenance switching between the two corresponding buses.

[0015] Preferably, the number of parallel transmission circuits connected to each onshore low-frequency collection bus is N+1. The power conversion devices of the N parallel transmission circuits are normal operating devices, and the power conversion device of the 1 parallel transmission circuit is a redundant device. The total rated transmission capacity of the N normal operating devices is not less than the rated installed capacity of all offshore wind farm clusters connected by the corresponding onshore low-frequency collection bus through the corresponding one or more low-frequency transmission submarine cables.

[0016] Preferably, when the AC converter is a non-MG unit, a voltage and frequency support device is connected to the COSCO-COSCO-Shanghai New Energy low-frequency collection and transmission topology and / or the low-frequency wind turbines connected to the offshore low-frequency collection bus are modified to have voltage / frequency support capability. When the AC converter is an MG unit, then in the COSCO Shipping New Energy Low Frequency Collection and Transmission Topology, one of the following methods is selected to provide voltage and frequency support to the offshore low frequency collection bus: (1) Neither connect to the voltage and frequency support device nor modify the low-frequency wind turbine connected to the offshore low-frequency collection bus; (2) Connect to the voltage and frequency support device; (3) Modify the low-frequency wind turbine connected to the offshore low-frequency collection bus to enable it to have voltage / frequency support capability; (4) Connect to the voltage and frequency support device and modify the low-frequency wind turbine connected to the offshore low-frequency collection bus to enable it to have voltage / frequency support capability.

[0017] When a voltage and frequency support device is added to the low-frequency collection and transmission topology of China Oceanwide New Energy, the voltage and frequency support device is connected to each return low-frequency collection bus. The voltage and frequency support device is used to control the voltage and frequency stability of the corresponding return low-frequency collection bus.

[0018] Preferably, the voltage and frequency support device is a grid-type power electronic device, a synchronous condenser, a grid-type energy storage device, or an energy router with grid control, or a series or parallel combination of any of the following: grid-type power electronic device, synchronous condenser, grid-type energy storage device, and energy router with grid control.

[0019] A second aspect of the present invention proposes a control method using the COSCO Shipping New Energy low-frequency collection and transmission topology described in the first aspect of the present invention, comprising: During normal operation, the energy router performs power flow control on the power of each low-frequency transmission submarine cable and the power of each parallel outgoing circuit through different modes; If the AC converter used as the power conversion device is an MG generator set, when a fault is detected on the side of a parallel output circuit connected to the power grid or user, it enters the fault ride-through control state. The fault ride-through control state controls the synchronous generator in the MG generator set corresponding to the faulty parallel output circuit to provide transient voltage and frequency support to the power grid or user. Determine whether the faulty parallel output circuit exceeds its corresponding overload capacity; if so, disconnect the MG units on the corresponding faulty parallel output circuit and perform power flow redistribution; after the faulty circuit is disconnected and the power flow is redistributed, if the fault is eliminated, put the MG units corresponding to the faulty parallel output circuit back into operation; otherwise, determine whether the offshore wind farm needs to be adjusted based on the overload status of the other N parallel output circuits; if so, the dispatcher will order a reduction in the output of the offshore wind farm.

[0020] Preferably, the energy router performs power flow control on the power of each low-frequency submarine transmission cable and the power of each parallel outgoing circuit through different modes, specifically: The system determines whether the wind power output of an offshore wind farm changes beyond a set threshold within a set time period. If so, the coarse adjustment condition is met. Alternatively, it determines whether the coarse adjustment condition is met based on the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable. If the coarse adjustment condition is met, the dispatch center determines whether the system needs to adjust its static stable operating point. If so, it enters the coarse adjustment mode, where each energy router redistributes the power of each low-frequency transmission submarine cable according to the coarse adjustment dispatch instructions issued by the dispatch center. Conversely, if the condition is not met, the circuit power imbalance is calculated based on the power of each parallel output circuit. The fine adjustment condition is then determined based on the circuit power imbalance. If so, the dispatch center or operation control center determines whether a short-term disturbance has occurred. If so, it enters the fine adjustment mode, where each energy router adjusts the power of its corresponding parallel output circuit according to the fine adjustment power instructions issued by the dispatch center or operation control center.

[0021] Preferably, the step of determining whether the coarse adjustment condition is met based on the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable specifically involves: The absolute value of the difference between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable is calculated as the power deviation of the corresponding low-frequency transmission submarine cable. If there is a low-frequency transmission submarine cable power deviation that is greater than the set first unbalance threshold coefficient multiplied by the average power of all low-frequency transmission submarine cables, then the coarse adjustment condition is met.

[0022] Preferably, the step of calculating the circuit power imbalance based on the power of each parallel output circuit, and determining whether the fine-tuning conditions are met based on the circuit power imbalance, specifically involves: Each low-frequency transmission submarine cable is configured to have multiple parallel outgoing circuits. The absolute value of the difference between the average power of all parallel outgoing circuits corresponding to each low-frequency transmission submarine cable and the power of each parallel outgoing circuit is calculated as the circuit power imbalance of the corresponding parallel outgoing circuit. If the circuit power imbalance of a parallel outgoing circuit exceeds the set second imbalance threshold coefficient multiplied by the average power of all parallel outgoing circuits corresponding to the corresponding low-frequency transmission submarine cable, then the fine-tuning condition is met.

[0023] Preferably, each energy router redistributes the power of each low-frequency submarine transmission cable according to the coarse adjustment scheduling instruction issued by the scheduling center, specifically as follows: Calculate the maximum transmission power and subtract the power of each parallel output circuit to obtain the adjustable power margin of the corresponding parallel output circuit; The dispatch center issues a coarse adjustment power command for each parallel outgoing circuit. The coarse adjustment power of each parallel outgoing circuit in the coarse adjustment power command satisfies the following: for each low-frequency transmission submarine cable, the sum of the coarse adjustment power of all corresponding parallel outgoing circuits is equal to the power deviation of the corresponding low-frequency transmission submarine cable; and the coarse adjustment power of the parallel outgoing circuit is less than or equal to the adjustable power margin of the corresponding parallel outgoing circuit; and the power of the corresponding parallel outgoing circuit before adjustment plus the coarse adjustment power of the corresponding parallel outgoing circuit is equal to the power of the low-frequency transmission submarine cable divided by the number of parallel outgoing circuits corresponding to the low-frequency transmission submarine cable. Each energy router adjusts the power of the corresponding parallel outgoing circuit according to the coarse adjustment power command.

[0024] Preferably, each energy router adjusts the power of its corresponding parallel output circuit according to the coarse or fine power adjustment command issued by the dispatch center, specifically as follows: The voltage at the beginning and end of the parallel transmission circuit is adjusted according to the issued coarse or fine adjustment power command. The voltage at the beginning of the parallel transmission circuit is multiplied by the voltage at the end of the parallel transmission circuit, divided by the reactance of the parallel transmission circuit, and then multiplied by the sine difference. This equals the coarse or fine adjustment power corresponding to the parallel transmission circuit. The sine difference is the sine value of the phase angle difference between the voltage at the beginning and end of the parallel transmission circuit after adjustment minus the sine value of the phase angle difference between the voltage at the beginning and end of the parallel transmission circuit before adjustment.

[0025] Preferably, the synchronous generator in the MG unit corresponding to the parallel output circuit controlling the fault provides transient voltage and frequency support to the power grid or user, specifically as follows: For the excitation device of the synchronous generator in the corresponding MG unit, the excitation control technology of automatic voltage regulator (AVR) is adopted to improve the terminal voltage of the MG unit and provide voltage support on the grid-connected side. At the same time, the inertia support capability of the synchronous generator is used to slow down the frequency drop, and the speed governor of the synchronous generator adjusts the frequency according to the speed deviation, together providing frequency support on the grid-connected side.

[0026] Preferably, the power flow redistribution specifically includes: Power flow control of each parallel output circuit is performed by the energy routers on the N parallel output circuits (excluding those affected by the fault) through different modes.

[0027] A third aspect of the present invention provides an apparatus comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor performing steps of a control method using the COSCO Shipping New Energy low-frequency collection and transmission topology described in the second aspect of the present invention.

[0028] The fourth aspect of the present invention provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the steps of the control method for the low-frequency collection and transmission topology of COSCO Shipping New Energy described in the second aspect of the present invention are used.

[0029] The beneficial effects of this invention are as follows: Compared with the prior art, it constructs an arbitrarily expandable offshore low-frequency gathering bus and an expandable offshore gathering platform / hub, enabling continuous access to offshore wind power capacity for multiple clusters and phases of projects, and unified collection and transmission at the tens of gigawatt level; through a modular low-frequency transmission-power converter transmission architecture, it achieves standardized configuration and rapid replication deployment for capacity expansion; it configures voltage / frequency support devices on the offshore low-frequency gathering bus to enhance bus strength and dynamic stability margin, thereby increasing the parallel connection of access capacity and transmission distance; and it implements controllable power flow allocation and balancing of low-frequency transmission submarine cables and transmission circuits through energy routers, combined with the redundant configuration of N+1 parallel circuits to form a hierarchical fault ride-through mechanism, reducing the risk of concentrated wind turbine disconnection under fault disturbances, and improving system operational reliability, equipment utilization, and project feasibility. Attached Figure Description

[0030] Figure 1 Topology diagram of COSCO Shipping New Energy's low-frequency collection and transmission when energy routers are connected in series; Figure 2 Topology diagram of COSCO Shipping New Energy's low-frequency collection and transmission when energy routers are connected in parallel; Figure 3 Detailed topology diagram of capacity expansion structure through combined transmission modules; Figure 4 A modular topology diagram for capacity expansion through combined transmission modules; Figure 5 Detailed topology diagram of the capacity expansion structure using flexible expansion modules; Figure 6 Detailed topology diagram of the collection and transmission of multiple offshore wind power collection busbars; Figure 7 Here is a flowchart of the power flow control process for the energy router. Figure 8 This is a flowchart of the fault crossing process. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0032] Embodiment 1 of this invention proposes a low-frequency collection and transmission topology for offshore renewable energy, comprising: an offshore low-frequency collection bus, a low-frequency transmission submarine cable, an onshore low-frequency collection bus, and multiple parallel transmission circuits, specifically: The output end of COSCO Shipping's offshore wind farm is connected to the offshore low-frequency collection bus. The offshore low-frequency collection bus collects the low-frequency AC power of each connected offshore wind farm and transmits it to the onshore low-frequency collection bus through a low-frequency transmission submarine cable. The onshore low-frequency collection bus is connected to the power grid or users through several parallel outgoing circuits. The onshore low-frequency collection bus is used to receive the low-frequency AC power transmitted from the low-frequency submarine cable and then distribute the power to each parallel outgoing circuit. The parallel outgoing circuit is composed of an energy router and a power conversion device or an energy router, a power conversion device and a transformer. If there is no transformer, the energy router is used as the preceding circuit. Otherwise, the energy router and the transformer are connected in different ways to form the preceding circuit. The onshore low-frequency collecting bus is connected to one side of the power conversion device through a preceding circuit, and the other side of the power conversion device is connected to the power grid or user. The power conversion device is an AC converter. The low-frequency transmission submarine cable, the onshore low-frequency collecting bus, and all parallel transmission circuits together form a combined transmission module.

[0033] The term "mid-sea" refers to the area within a defined distance from the shoreline.

[0034] It should be noted that the functions of each component in the device are as follows: Energy router: used to realize power flow distribution and power balancing among multiple parallel outgoing circuits or multiple low-frequency submarine power transmission cables; Transformer: Used for voltage transformation and electrical isolation; Power conversion device: Its motor side is connected to the transformer (low-frequency side electrical connection), and the generator side outputs power frequency AC power.

[0035] In this preferred embodiment, the energy router and the transformer are connected in different ways to form a preceding circuit, specifically: Energy routers can be connected in series or parallel. When connected in series, such as... Figure 1 As shown, the energy router, transformer, and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user (i.e., one end of the energy router is connected to the low-voltage side of the transformer), or the transformer, energy router, and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user (i.e., one end of the energy router is connected to the high-voltage side of the transformer). When connected in parallel, such as Figure 2 As shown, the transformer and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user. The energy router is connected between the high-voltage side or low-voltage side of the transformer and the system reference point. It should be noted that... Figure 2 This is a schematic diagram of an energy router connected to the low-voltage side of a transformer.

[0036] It should be noted that the connection between one end of the energy router and the low-voltage or high-voltage side of the transformer can be freely chosen. The high-voltage side is suitable for energy routers with low current resistance and high voltage resistance, while the low-voltage side is suitable for situations with high current resistance and low voltage resistance. This embodiment adopts... Figure 1 This is the most feasible and general scenario when reimplementing the system.

[0037] In this preferred embodiment, the power conversion device in the parallel output circuit is an AC converter that converts low-frequency AC power into power-frequency AC power. The AC converter includes: an MG generator set, a modular multilevel matrix converter (M3C), and any combination thereof. When the AC converter is an MG generator set, the MG generator set includes a motor and a generator, which are coaxially connected and perform electromechanical energy transfer. The motor side of the MG generator set is electrically connected to the onshore low-frequency collecting bus, and the generator side of the MG generator set outputs power-frequency AC power and is electrically connected to the power grid or user side. The motor and / or generator is any combination of synchronous motors or asynchronous motors.

[0038] Optionally, the motor-side frequency and generator-side frequency of the MG unit are matched through the relationship between the number of pole pairs and the rotational speed, and the number of pole pairs is set to satisfy:

[0039] in, p denoted as the number of pole pairs in the rotating magnetic field of the motor; f For the corresponding side power supply frequency; This represents the motor speed.

[0040] In this preferred embodiment, when the wind power capacity connected to the offshore low-frequency collection bus exceeds the transmission capacity limit of a single-circuit low-frequency transmission submarine cable, the capacity of the COSCO-COSCO new energy low-frequency collection and transmission topology is expanded by adding a combined transmission module or a flexible DC extension module between the offshore low-frequency collection bus and the power grid or user.

[0041] like Figure 3 and Figure 4 As shown, in this preferred embodiment, the capacity of the COSCO-COSCO offshore new energy low-frequency collection and transmission topology is expanded by adding a combined transmission module between the offshore low-frequency collection bus and the power grid or user. Specifically: Several combined transmission modules are added, and all combined transmission modules are connected in parallel between the offshore low-frequency collection bus and the power grid or user. The total number of combined transmission modules after the addition is greater than or equal to the wind power capacity connected to the offshore low-frequency collection bus divided by the transmission capacity limit of a single low-frequency submarine cable.

[0042] It should be noted that all combined transmission modules are connected in parallel between the offshore low-frequency collection bus and the power grid or users. Specifically, the offshore low-frequency collection bus is connected in parallel to multiple low-frequency submarine transmission cables; each low-frequency submarine transmission cable connects to its corresponding onshore low-frequency collection bus after landing; and each onshore low-frequency collection bus is then connected to the power grid through its corresponding set of parallel transmission circuits. By connecting multiple combined transmission modules in parallel, near-linear capacity expansion can be achieved without changing the original basic transmission topology, thus supporting the centralized transmission of tens of gigawatts of offshore wind power.

[0043] like Figure 5 As shown, the capacity of the COSCO Shipping New Energy Low-Frequency Aggregation and Transmission Topology is expanded by adding a flexible DC extension module between the offshore low-frequency aggregation bus and the power grid or user. Specifically: The offshore low-frequency collection bus is connected to the power grid or users by connecting at least one flexible DC transmission branch. The flexible DC transmission branch consists of an offshore converter, a DC transmission submarine cable, and an onshore converter. The offshore low-frequency collection bus is connected to the input end of the offshore converter. The offshore converter and the onshore converter are connected by a DC transmission submarine cable. The output end of the onshore converter is connected to the power grid or users.

[0044] like Figure 6 As shown, in this preferred embodiment, the number of offshore low-frequency collection buses is set to one or more. The offshore low-frequency collection buses are located on an offshore collection platform, which is an expandable offshore collection platform. When there are multiple offshore low-frequency collection buses, the offshore collection platforms they are connected to can be one or more. When a new offshore wind farm is added, a new offshore low-frequency collection bus is selected and the new offshore wind farm is connected to the new offshore low-frequency collection bus, or the new offshore wind farm is connected to the existing offshore low-frequency collection bus, and the number of access ports and collection capacity of the corresponding offshore low-frequency collection bus are expanded. When a new offshore wind farm is added, the corresponding offshore collection platform is expanded simultaneously.

[0045] Furthermore, the offshore aggregation platform can be expanded into an aggregation hub serving both offshore and deep-sea wind power. Through the coordinated expansion of the offshore aggregation platform and the offshore low-frequency aggregation bus, continuous access and unified aggregation and transmission of offshore wind power capacity from multiple clusters and multiple phases of projects can be achieved, with the aggregation scale expandable to tens of gigawatts.

[0046] It should be noted that when there are multiple offshore low-frequency collection buses, it is also necessary to determine whether to expand the capacity. When the wind power capacity connected to the same offshore low-frequency collection bus exceeds the transmission capacity limit of a single low-frequency submarine cable, the capacity of COSCO Shipping New Energy's low-frequency collection and transmission topology can be expanded by adding a combined transmission module between the corresponding offshore low-frequency collection bus and the power grid or user.

[0047] In this embodiment, a bus tie switch is preferably set between different return low-frequency collection buses at sea and between different return low-frequency collection buses at shore. The bus tie switch is used to selectively connect or separate the two corresponding buses to perform power mutual assistance, operation mode reconfiguration or maintenance switching between the two corresponding buses.

[0048] In this preferred embodiment, the number of parallel transmission circuits connected to each onshore low-frequency collection bus is N+1. The power conversion devices of the N parallel transmission circuits are operating normally, and the power conversion device of the one parallel transmission circuit is a redundant device. The total rated transmission capacity of the N operating devices is not less than the rated installed capacity of all offshore wind farm clusters connected to the corresponding onshore low-frequency collection bus via one or more corresponding low-frequency submarine cables. The redundant device participates in operation under normal conditions to share power flow and reduce single-circuit current and thermal stress. When any power conversion device is under maintenance or fails, the remaining power conversion devices and the redundant device share the transmission power, effectively preventing severe overload of other devices or a sudden drop in system transmission capacity due to the failure of a single power conversion device. This significantly improves system reliability, maintenance flexibility, and fault ride-through capability.

[0049] It should be noted that in actual engineering implementation, not all of the N+1 parallel outgoing circuits need to be equipped with energy routers. In one optional implementation, energy routers can be configured only on the low-frequency side of any N parallel outgoing circuits, while the remaining parallel outgoing circuit is not equipped with an energy router. Since the parallel system satisfies power balance constraints, given a fixed total outgoing power, the power of the branch without an energy router can be uniquely determined by the difference between the total power and the power of the N controlled branches. Therefore, adjusting the power of any N branches is equivalent to constraining and controlling the power flow distribution of the N+1 parallel outgoing circuits. Furthermore, when energy routers are configured only on any N parallel outgoing circuits, the system's cable-level power redistribution capability for multiple low-frequency submarine transmission cables can be optional or not performed. In this case, the power flow deviation between multiple submarine cables can achieve self-balancing under steady-state conditions through the negative feedback mechanism formed by the resistance change caused by line loss and temperature rise.

[0050] In this preferred embodiment, when the AC converter is a non-MG unit, a voltage and frequency support device is connected to the COSCO-COSCO-Shanghai New Energy low-frequency collection and transmission topology and / or the low-frequency wind turbines connected to the offshore low-frequency collection bus are modified to have voltage / frequency support capability. When the AC converter is an MG unit, then in the COSCO Shipping New Energy Low Frequency Collection and Transmission Topology, one of the following methods is selected to provide voltage and frequency support to the offshore low frequency collection bus: (1) Neither connect to the voltage and frequency support device nor modify the low-frequency wind turbine connected to the offshore low-frequency collection bus; (2) Connect to the voltage and frequency support device; (3) Modify the low-frequency wind turbine connected to the offshore low-frequency collection bus to enable it to have voltage / frequency support capability; (4) Connect to the voltage and frequency support device and modify the low-frequency wind turbine connected to the offshore low-frequency collection bus to enable it to have voltage / frequency support capability.

[0051] When a voltage and frequency support device is added to the low-frequency collection and transmission topology of China Oceanwide New Energy, the voltage and frequency support device is connected to each return low-frequency collection bus. The voltage and frequency support device is used to control the voltage and frequency stability of the corresponding return low-frequency collection bus.

[0052] In this preferred embodiment, the voltage and frequency support device is a grid-type power electronic device, a synchronous condenser, a grid-type energy storage device, or an energy router with grid control, or a series or parallel combination of any of the following: grid-type power electronic device, synchronous condenser, grid-type energy storage device, and energy router with grid control.

[0053] Embodiment 2 of the present invention performs simulation control based on the construction and accumulation sequence of offshore wind farms in locations A and B.

[0054] In the initial stage of construction, several offshore wind farms exist in area A of the Zhonghai sea area. At this time, only one offshore low-frequency collection bus is selected (it can be set to multiple circuits). The output terminals of these offshore wind farms are connected to the offshore low-frequency collection bus 1 located in Zhonghai. The offshore low-frequency collection bus 1 collects the low-frequency AC power from each offshore wind farm and transmits it to the onshore low-frequency collection bus through a low-frequency transmission submarine cable. All parallel output circuits are connected in parallel to the onshore low-frequency collection bus. The onshore low-frequency collection bus receives the low-frequency AC power transmitted from the low-frequency transmission submarine cable and then distributes the power to each parallel output circuit. In this embodiment, the power conversion devices in the parallel output circuits at area A are all MG units.

[0055] During the mid-term construction phase, with the development of offshore wind power, several new offshore wind farms will be developed in the Zhonghai sea area. When adding m offshore wind farms at location A in Zhonghai, the existing offshore low-frequency collection bus 1 will be selected for connection, and the wind power capacity connected to the offshore low-frequency collection bus 1 will not exceed the transmission capacity limit of a single-circuit low-frequency submarine cable. The number of access ports and collection capacity of the offshore low-frequency collection bus 1 will be expanded normally, and the offshore collection platform will be expanded simultaneously. When the (m+1)th wind farm is introduced, the wind power capacity connected to the offshore low-frequency collection bus 1 will exceed the single-circuit transmission capacity limit of the submarine cable. To limit the transmission capacity of the low-frequency submarine power transmission cable, in addition to expanding the number of access ports and collection capacity of the offshore low-frequency collection bus 1, and simultaneously expanding the offshore collection platform, capacity expansion is also carried out by adding several combined transmission modules. All offshore wind farm outputs are connected to the offshore low-frequency collection bus 1, and all combined transmission modules are connected in parallel between the offshore low-frequency collection bus 1 and the power grid. The total number of combined transmission modules after the addition is greater than or equal to the wind power capacity connected to the offshore low-frequency collection bus 1 divided by the transmission capacity limit of a single low-frequency submarine power transmission cable. Furthermore, bus tie switches are installed between different onshore low-frequency collection buses.

[0056] During the later stages of construction, offshore wind power will be gradually developed from the central sea area to the open sea. Several offshore wind farms will be developed in location B in the open sea area. At this time, instead of connecting to the original offshore low-frequency collection bus 1, an additional offshore low-frequency collection bus 2 will be added to connect and collect offshore wind power. If the offshore low-frequency collection bus 2 needs to be expanded in capacity, the capacity expansion method will be the same as that in location A.

[0057] For location A, considering economic efficiency, the offshore low-frequency collection bus 1 will not be equipped with additional voltage and frequency support devices. Instead, the voltage and frequency of the offshore low-frequency bus will be supported by the excitation device and speed governor installed on the MG unit, combined with the inherent rotational inertia of the MG unit. For location B, it is permissible to add voltage and frequency support devices to the COSCO-COSCO-Shanghai new energy low-frequency collection and transmission topology to achieve voltage and frequency stability of the offshore low-frequency collection bus. This embodiment expands the device according to the construction and expansion sequence. Even in the final long-distance, large-capacity construction scenario, it still ensures the technical economy and scalability of the mid-to-far offshore low-frequency collection and transmission topology, supporting the rolling development and large-scale collection of offshore wind power from nearshore to mid-to-far and offshore areas.

[0058] Embodiment 3 of the present invention proposes a control method using the COSCO Shipping New Energy low-frequency collection and transmission topology described in Embodiment 1 of the present invention, including: like Figure 7 As shown, during normal operation, the energy router performs power flow control on the power of each low-frequency transmission submarine cable and the power of each parallel outgoing circuit through different modes. like Figure 8As shown, if the AC converter used as the power conversion device is an MG generator set, when a fault is detected on the side of a parallel output circuit connected to the power grid or user, it enters the fault ride-through control state. The fault ride-through control state controls the synchronous generator in the MG generator set corresponding to the faulty parallel output circuit to provide transient voltage and frequency support to the power grid or user. Determine whether the faulty parallel output circuit exceeds its corresponding overload capacity; if so, disconnect the MG units on the corresponding faulty parallel output circuit and perform power flow redistribution; after the faulty circuit is disconnected and the power flow is redistributed, if the fault is eliminated, put the MG units corresponding to the faulty parallel output circuit back into operation; otherwise, determine whether the offshore wind farm needs to be adjusted based on the overload status of the other N parallel output circuits; if so, the dispatcher will order a reduction in the output of the offshore wind farm.

[0059] It should be noted that the energy router supports series or parallel access and is used to coordinate and regulate the power flow on the low-frequency side to achieve active and controllable distribution of the system power flow. The energy router takes into account the following two types of power flow regulation functions: one is power flow regulation and equalization distribution for multiple low-frequency AC transmission submarine cables, and the other is power flow equalization and deviation suppression for parallel output circuits, specifically: (1) Power flow regulation function for multiple low-frequency AC transmission submarine cables When the offshore low-frequency collection bus transmits power to the shore through multiple low-frequency AC transmission submarine cables, the differences in cable length due to different landing points, or factors such as long-term large fluctuations in offshore renewable energy output and changes in the operating status of parallel systems, may cause problems such as uneven power flow distribution, insufficient overload margin of a single circuit, or tidal power bias among different low-frequency AC transmission submarine cables.

[0060] In this invention, there is no need to add a dedicated power flow control device to the low-frequency power transmission submarine cable. The energy routers in each parallel transmission circuit can actively adjust the injection power of the low-frequency gathering bus on shore through a coordinated adjustment method, thereby realizing the active adjustment and balanced distribution of the power flow of each low-frequency AC power transmission submarine cable.

[0061] (2) Power flow balancing function for parallel output circuits When there are many parallel transmission circuits and the parameters of each circuit (such as line length, distributed impedance, capacitance to ground, etc.) differ, or when there are short-term disturbances in the marine renewable energy, it is easy to cause uneven power flow distribution between transmission circuits, resulting in excessive current and increased thermal stress in some circuits, which reduces the reliability and safety of the system power supply and may even threaten the overall stability of the transmission system.

[0062] In this scenario, the energy routers configured in each loop can adjust the power of their respective loops, thereby achieving power flow balance and deviation suppression between parallel loops, and improving system stability and equipment utilization.

[0063] Therefore, to accommodate both of these functions, the energy router has at least two modes: coarse adjustment and fine adjustment. In this preferred embodiment, the energy router performs power flow control on the power of each low-frequency transmission submarine cable and the power of each parallel outgoing circuit through different modes, specifically: If it is determined that there are long-term (tens of seconds / minutes) large power output fluctuations in new energy sources, or if the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable is used to determine whether the coarse adjustment conditions are met, then the coarse adjustment conditions are met. The dispatch center then determines whether the system needs to adjust the static stable operating point. If so, the system enters the coarse adjustment mode.

[0064] The coarse adjustment mode involves each energy router redistributing the power of each low-frequency power transmission submarine cable according to the coarse adjustment scheduling instructions issued by the scheduling center. Conversely, the power imbalance of the circuit is calculated based on the power of each parallel output circuit. The power imbalance of the circuit is used to determine whether the fine adjustment conditions are met. If they are met, the dispatch center or operation control center determines whether a short-term (millisecond / second-level) disturbance has occurred. If so, the fine adjustment mode is entered. The fine-tuning mode involves each energy router adjusting the power of its corresponding parallel output circuit according to the fine-tuning power command issued by the scheduling center or operation control center.

[0065] In this preferred embodiment, the step of determining whether the coarse adjustment condition is met based on the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable specifically involves: The absolute value of the difference between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable is calculated as the power deviation of the corresponding low-frequency transmission submarine cable. The formula is as follows:

[0066]

[0067] in, M This represents the total number of low-frequency power transmission submarine cables. P a,K The average power of all low-frequency submarine transmission cables. P k For the first k The power of the low-frequency transmission submarine cable, Δ P k For the first k Power deviation of low-frequency transmission submarine cable.

[0068] If the power deviation of a low-frequency transmission submarine cable exceeds the set first unbalance threshold coefficient multiplied by the average power of all low-frequency transmission submarine cables, then the coarse adjustment condition is met, as shown in the formula:

[0069] in, This is the set first imbalance threshold coefficient; In this preferred embodiment, the step of calculating the circuit power imbalance based on the power of each parallel output circuit, and determining whether the fine-tuning conditions are met based on the circuit power imbalance, specifically involves: Each low-frequency transmission submarine cable is configured with multiple parallel outgoing circuits. The absolute value of the difference between the average power of all parallel outgoing circuits corresponding to each low-frequency transmission submarine cable and the power of each parallel outgoing circuit is used as the circuit power imbalance of the corresponding parallel outgoing circuit. The formula is: ;

[0070] in, This represents the average power of all parallel outgoing circuits corresponding to the low-frequency power transmission submarine cable; This represents the total number of all parallel outgoing circuits corresponding to the low-frequency submarine power transmission cable. The first corresponding to low-frequency submarine power transmission cable The power of the parallel output circuit; The first corresponding to low-frequency submarine power transmission cable The difference between the average power of the parallel output circuits and the power of each corresponding parallel output circuit. The absolute value is the first The power imbalance of parallel output circuits.

[0071] If the power imbalance of a parallel transmission circuit exceeds the set second imbalance threshold coefficient multiplied by the average power of all parallel transmission circuits corresponding to the low-frequency submarine transmission cable, then the fine-tuning condition is met, as shown in the formula:

[0072] in, This is the second imbalance threshold coefficient.

[0073] In this preferred embodiment, each energy router redistributes the power of each low-frequency submarine transmission cable according to the coarse adjustment scheduling instruction issued by the scheduling center, specifically as follows: The adjustable power margin of the corresponding parallel output circuit is obtained by subtracting the power of each parallel output circuit from the maximum transmission power, using the following formula:

[0074] in, For the first k The first corresponding low-frequency transmission submarine cable i Adjustable power margin of the parallel output circuit. For the firstk The first corresponding low-frequency transmission submarine cable i The maximum transmission power of the parallel output circuit; The dispatch center issues a coarse adjustment power command for each parallel outgoing circuit. The coarse adjustment power of each parallel outgoing circuit in the coarse adjustment power command satisfies the following conditions: for each low-frequency transmission submarine cable, the sum of the coarse adjustment power of all corresponding parallel outgoing circuits equals the power deviation of the corresponding low-frequency transmission submarine cable; and the coarse adjustment power of the parallel outgoing circuit is less than or equal to the adjustable power margin of the corresponding parallel outgoing circuit; and the power of the corresponding parallel outgoing circuit before adjustment plus the coarse adjustment power of the corresponding parallel outgoing circuit equals the power of the low-frequency transmission submarine cable divided by the number of parallel outgoing circuits corresponding to the low-frequency transmission submarine cable. Each energy router adjusts the power of the corresponding parallel outgoing circuit according to the coarse adjustment power command, using the following formula:

[0075] in, This is for coarse adjustment of power.

[0076] In this preferred embodiment, each energy router adjusts the power of its corresponding parallel output circuit according to the coarse or fine power adjustment command issued by the dispatch center or operation control center, specifically as follows: The voltage at the beginning and end of the parallel transmission circuit is adjusted according to the issued coarse or fine adjustment power command. The voltage at the beginning of the parallel transmission circuit multiplied by the voltage at the end of the parallel transmission circuit, divided by the reactance of the parallel transmission circuit, and then multiplied by the sine difference, equals the corresponding coarse or fine adjustment power of the parallel transmission circuit. The sine difference is the sine value of the phase angle difference between the voltage at the beginning and end of the corresponding parallel transmission circuit after adjustment minus the sine value of the phase angle difference between the voltage at the beginning and end of the corresponding parallel transmission circuit before adjustment. The formula is:

[0077] in, This refers to the corresponding coarse or fine adjustment power; , This refers to the voltage at the beginning and end of the circuit. Before adjustment of the phase angle difference between the beginning and end points, To adjust the phase angle difference between the beginning and end, This refers to the reactance of the circuit.

[0078] In summary, since a single low-frequency transmission submarine cable corresponds to multiple parallel outgoing circuits, and the energy routers of each circuit jointly undertake the power regulation task of the submarine cable, the system adopts an allocation mechanism in coarse adjustment mode: first, the total power bias at the submarine cable level to be adjusted is determined based on the power deviation of each low-frequency transmission submarine cable; then, combined with the power margin and operating status of each parallel circuit, the total bias at the submarine cable level is allocated to the energy routers of each circuit, so as to complete the redistribution of submarine cable power while avoiding the circuit load from exceeding the allowable range. Furthermore, considering factors such as inconsistent line parameters of each parallel circuit or short-term disturbances in offshore renewable energy sources, which may lead to uneven power flow distribution in the parallel circuits, fine adjustment compensation commands can be generated based on the circuit power imbalance to achieve power flow balance among the parallel circuits.

[0079] In this preferred embodiment, the synchronous generator in the MG unit corresponding to the parallel output circuit controlling the fault provides transient voltage and frequency support to the power grid or user, specifically as follows: For the excitation device of the synchronous generator in the corresponding MG unit, the excitation control technology of automatic voltage regulator (AVR) is adopted to improve the terminal voltage of the MG unit and provide voltage support on the grid-connected side. At the same time, the inertia support capability of the synchronous generator is used to slow down the frequency drop, and the speed governor of the synchronous generator adjusts the frequency according to the speed deviation, together providing frequency support on the grid-connected side.

[0080] In this preferred embodiment, the power flow redistribution specifically refers to: Power flow control of each parallel output circuit is performed by the energy routers on the N parallel output circuits (excluding those affected by the fault) through different modes.

[0081] In this preferred embodiment, determining whether the parallel output circuit has exceeded its corresponding overload capacity specifically involves: If the stator current value of the synchronous generator in the corresponding MG unit of the parallel output circuit reaches a set multiple of the rated current and the duration exceeds the set timeout threshold, it is considered that the corresponding parallel output circuit has exceeded the corresponding overload capacity.

[0082] Specifically, judging whether the parallel output circuit exceeds the corresponding overload capacity is only a preferred option in this embodiment. There are other judgment methods in engineering. In this embodiment, the stator current is set to 1.5 times and the corresponding timeout threshold is 2 minutes.

[0083] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0084] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0085] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0086] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. COSCO Marine New Energy Low Frequency Gathering and Sending Topology, comprising: The system comprises a marine low-frequency collection busbar, a low-frequency transmission submarine cable, an onshore low-frequency collection busbar, and multiple parallel transmission circuits, characterized in that: The output end of COSCO Shipping's offshore wind farm is connected to the offshore low-frequency collection bus. The offshore low-frequency collection bus collects the low-frequency AC power of each connected offshore wind farm and transmits it to the onshore low-frequency collection bus through a low-frequency transmission submarine cable. The onshore low-frequency collection bus is connected to the power grid or users through several parallel outgoing circuits. The onshore low-frequency collection bus is used to receive the low-frequency AC power transmitted from the low-frequency submarine cable and then distribute the power to each parallel outgoing circuit. The parallel outgoing circuit is composed of an energy router and a power conversion device or an energy router, a power conversion device and a transformer. If there is no transformer, the energy router is used as the preceding circuit. Otherwise, the energy router and the transformer are connected in different ways to form the preceding circuit. The onshore low-frequency collection bus is connected to one side of the power conversion device via a preceding circuit, and the other side of the power conversion device is connected to the power grid or a user. The power conversion device is an AC converter, comprising: an MG generator unit, a modular multilevel matrix converter (M3C), and any combination thereof. The low-frequency transmission submarine cable, the onshore low-frequency collection bus, and all parallel outgoing circuits together form a combined transmission module. When the wind power capacity connected to the offshore low-frequency collection bus exceeds the transmission capacity limit of a single-circuit low-frequency transmission submarine cable, the capacity of the COSCO-COSCO offshore new energy low-frequency collection and transmission topology is expanded by adding a combined transmission module or a flexible DC extension module between the offshore low-frequency collection bus and the power grid or user. The energy router is used to coordinate and regulate the power flow on the low-frequency side, achieving active and controllable distribution of system power flow, regulating and balancing power flow for multiple low-frequency AC transmission submarine cables, and balancing power flow for parallel outgoing circuits. Deviation Suppression: This involves determining whether the wind power output of an offshore wind farm changes beyond a set threshold within a set time period, or judging whether coarse adjustment conditions are met based on the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable. If the coarse adjustment conditions are met, the dispatch center determines whether the system needs to adjust its static stable operating point. If so, it enters coarse adjustment mode, where each energy router redistributes the power of each low-frequency transmission submarine cable according to the coarse adjustment dispatch instructions issued by the dispatch center. Conversely, if the conditions are not met, the circuit power imbalance is calculated based on the power of each parallel output circuit. The fine adjustment conditions are then determined based on the circuit power imbalance. If so, the dispatch center or operation control center determines whether a short-term disturbance has occurred. If so, it enters fine adjustment mode, where each energy router adjusts the power of its corresponding parallel output circuit according to the fine adjustment power instructions issued by the dispatch center or operation control center.

2. The COSCO Shipping New Energy Low-Frequency Aggregation and Transmission Topology according to claim 1, characterized in that: The energy router and transformer form a preceding circuit through different connection methods, specifically: The energy router can be connected in series or in parallel. When connected in series, the energy router, transformer, and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user, or the transformer, energy router, and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user. When connected in parallel, the transformer and AC converter are connected in series between the onshore low-frequency collection bus and the power grid or user, and the energy router is connected between the high-voltage side or low-voltage side of the transformer and the system reference point.

3. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 2, characterized in that: The power conversion device in the parallel output circuit is an AC converter that converts low-frequency AC power into power-frequency AC power. When the AC converter is an MG unit, the MG unit includes a motor and a generator, which are coaxially connected and perform electromechanical energy transfer. The motor side of the MG unit is electrically connected to the onshore low-frequency collecting bus, and the generator side of the MG unit outputs power-frequency AC power and is electrically connected to the power grid or user side. The motor and / or generator can be any combination of synchronous motors or asynchronous motors.

4. The COSCO Shipping New Energy Low-Frequency Aggregation and Transmission Topology according to claim 1, characterized in that: When expanding the capacity of the COSCO Shipping New Energy low-frequency collection and transmission topology by adding combined transmission modules or flexible DC expansion modules between the offshore low-frequency collection bus and the power grid or users; the energy router performs power flow control on the power of each low-frequency transmission submarine cable and the power of each parallel transmission circuit through different modes: Determine whether the change in wind power output of an offshore wind farm exceeds a set threshold within a set time period, or determine whether the coarse adjustment conditions are met based on the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable. If the coarse adjustment conditions are met, the dispatch center determines whether the system needs to adjust its static stable operating point. If so, it enters the coarse adjustment mode, and each energy router redistributes the power of each low-frequency transmission submarine cable according to the coarse adjustment dispatch instructions issued by the dispatch center. Otherwise, the power imbalance of the circuit is calculated based on the power of each parallel output circuit. The power imbalance is then used to determine whether the fine-tuning conditions are met. If the fine-tuning conditions are met, the dispatch center or operation control center determines whether a short-term disturbance has occurred. If a short-term disturbance has occurred, the fine-tuning mode is entered, and each energy router adjusts the power of its corresponding parallel output circuit according to the fine-tuning power command issued by the dispatch center or operation control center. If the fine-tuning conditions are not met, the current operating state is maintained.

5. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 4, characterized in that: The capacity of the COSCO Shipping New Energy Low-Frequency Aggregation and Transmission Topology is expanded by adding a combined transmission module between the offshore low-frequency aggregation bus and the power grid or users. Specifically: Several combined transmission modules are added, and all combined transmission modules are connected in parallel between the offshore low-frequency collection bus and the power grid or user. The total number of combined transmission modules after the addition is greater than or equal to the wind power capacity connected to the offshore low-frequency collection bus divided by the transmission capacity limit of a single low-frequency submarine cable.

6. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 5, characterized in that: The capacity of COSCO Shipping New Energy's low-frequency collection and transmission topology is expanded by adding a flexible DC extension module between the offshore low-frequency collection bus and the power grid or users. Specifically: The offshore low-frequency collection bus is connected to the power grid or users by connecting at least one flexible DC transmission branch. The flexible DC transmission branch consists of an offshore converter, a DC transmission submarine cable, and an onshore converter. The offshore low-frequency collection bus is connected to the input end of the offshore converter. The offshore converter and the onshore converter are connected by a DC transmission submarine cable. The output end of the onshore converter is connected to the power grid or users.

7. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 6, characterized in that: The number of offshore low-frequency collection buses is set to one or more. The offshore low-frequency collection buses are set on the offshore collection platform. When a new offshore wind farm is added, a new offshore low-frequency collection bus is selected and the new offshore wind farm is connected to the new offshore low-frequency collection bus, or the new offshore wind farm is connected to the existing offshore low-frequency collection bus, and the number of access ports and collection capacity of the corresponding offshore low-frequency collection bus are expanded. When a new offshore wind farm is added, the corresponding offshore collection platform is expanded simultaneously.

8. The COSCO Shipping New Energy Low-Frequency Aggregation and Transmission Topology according to claim 7, characterized in that: Bus tie switches are installed between different offshore low-frequency collection buses and between different onshore low-frequency collection buses. The bus tie switches are used to selectively connect or separate the two corresponding buses to perform power mutual assistance, operation mode reconfiguration or maintenance switching between the two corresponding buses.

9. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 8, characterized in that: The number of parallel transmission circuits connected to each onshore low-frequency collection bus is N+1. The power conversion devices of the N parallel transmission circuits are normal operating devices, and the power conversion device of the 1 parallel transmission circuit is a redundant device. The total rated transmission capacity of the N normal operating devices is not less than the rated installed capacity of all offshore wind farm clusters connected by the corresponding onshore low-frequency collection bus through the corresponding one or more low-frequency transmission submarine cables.

10. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 4, characterized in that: When the AC converter is a non-MG unit, a voltage and frequency support device is connected to the COSCO Shipping New Energy low-frequency collection and transmission topology and / or the low-frequency wind turbine connected to the offshore low-frequency collection bus is modified to enable it to have voltage and frequency support capability. When the AC converter is an MG unit, then in the COSCO Shipping New Energy Low Frequency Collection and Transmission Topology, one of the following methods is selected to provide voltage and frequency support to the offshore low frequency collection bus: (1) Neither connect to the voltage and frequency support device nor modify the low-frequency wind turbine connected to the offshore low-frequency collection bus; (2) Connect to the voltage and frequency support device; (3) Modify the low-frequency wind turbine connected to the offshore low-frequency collection bus to enable it to have voltage and frequency support capability; (4) Connect to the voltage and frequency support device and modify the low-frequency wind turbine connected to the offshore low-frequency collection bus to enable it to have voltage / frequency support capability. When a voltage and frequency support device is added to the low-frequency collection and transmission topology of China Oceanwide New Energy, the voltage and frequency support device is connected to each return low-frequency collection bus. The voltage and frequency support device is used to control the voltage and frequency stability of the corresponding return low-frequency collection bus.

11. The COSCO Shipping New Energy Low-Frequency Collection and Transmission Topology according to claim 10, characterized in that: The voltage and frequency support device is a grid-type power electronic device, a synchronous condenser, a grid-type energy storage device, or an energy router with grid control, or a series or parallel combination of any of the following: grid-type power electronic device, synchronous condenser, grid-type energy storage device, and energy router with grid control.

12. The method of claim 8-11, wherein the method is used for the control of a topology of offshore new energy low-frequency collection and sending-out, characterized in that, include: During normal operation, the energy router performs power flow control on the power of each low-frequency transmission submarine cable and the power of each parallel outgoing circuit through different modes; If the AC converter used as the power conversion device is an MG generator set, when a fault is detected on the side of a parallel output circuit connected to the power grid or user, it enters the fault ride-through control state. The fault ride-through control state controls the synchronous generator in the MG generator set corresponding to the faulty parallel output circuit to provide transient voltage and frequency support to the power grid or user. Determine whether the faulty parallel output circuit exceeds its corresponding overload capacity; if so, disconnect the MG units on the corresponding faulty parallel output circuit and perform power flow redistribution; after the faulty circuit is disconnected and the power flow is redistributed, if the fault is eliminated, put the MG units corresponding to the faulty parallel output circuit back into operation; otherwise, determine whether the offshore wind farm needs to be adjusted based on the overload status of the other N parallel output circuits; if so, the dispatcher will order a reduction in the output of the offshore wind farm.

13. The control method for the COSCO Shipping New Energy Low-Frequency Gathering and Transmission Topology according to claim 12, characterized in that: The determination of whether the coarse adjustment condition is met based on the deviation between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable is as follows: The absolute value of the difference between the average power of all low-frequency transmission submarine cables and the power of each low-frequency transmission submarine cable is calculated as the power deviation of the corresponding low-frequency transmission submarine cable. If there is a low-frequency transmission submarine cable power deviation that is greater than the set first unbalance threshold coefficient multiplied by the average power of all low-frequency transmission submarine cables, then the coarse adjustment condition is met.

14. The control method for the COSCO Shipping New Energy Low-Frequency Gathering and Transmission Topology according to claim 12, characterized in that: The calculation of circuit power imbalance based on the power of each parallel output circuit, and the determination of whether the fine-tuning conditions are met based on the circuit power imbalance, specifically involves: Each low-frequency transmission submarine cable is configured to have multiple parallel outgoing circuits. The absolute value of the difference between the average power of all parallel outgoing circuits corresponding to each low-frequency transmission submarine cable and the power of each parallel outgoing circuit is calculated as the circuit power imbalance of the corresponding parallel outgoing circuit. If the circuit power imbalance of a parallel outgoing circuit exceeds the set second imbalance threshold coefficient multiplied by the average power of all parallel outgoing circuits corresponding to the corresponding low-frequency transmission submarine cable, then the fine-tuning condition is met.

15. The control method for the COSCO Shipping New Energy Low-Frequency Gathering and Transmission Topology according to claim 13, characterized in that: Each energy router redistributes the power of each low-frequency submarine transmission cable according to the coarse adjustment scheduling instructions issued by the dispatch center, specifically as follows: Calculate the maximum transmission power and subtract the power of each parallel output circuit to obtain the adjustable power margin of the corresponding parallel output circuit; The dispatch center issues a coarse adjustment power command for each parallel outgoing circuit. The coarse adjustment power of each parallel outgoing circuit in the coarse adjustment power command satisfies the following: for each low-frequency transmission submarine cable, the sum of the coarse adjustment power of all corresponding parallel outgoing circuits is equal to the power deviation of the corresponding low-frequency transmission submarine cable; and the coarse adjustment power of the parallel outgoing circuit is less than or equal to the adjustable power margin of the corresponding parallel outgoing circuit; and the power of the corresponding parallel outgoing circuit before adjustment plus the coarse adjustment power of the corresponding parallel outgoing circuit is equal to the power of the low-frequency transmission submarine cable divided by the number of parallel outgoing circuits corresponding to the low-frequency transmission submarine cable. Each energy router adjusts the power of the corresponding parallel outgoing circuit according to the coarse adjustment power command.

16. The control method for the COSCO Shipping New Energy Low-Frequency Gathering and Transmission Topology according to claim 15, characterized in that: Each energy router adjusts the power of its corresponding parallel output circuit according to the coarse or fine power adjustment instructions issued by the dispatch center, specifically as follows: The voltage at the beginning and end of the parallel transmission circuit is adjusted according to the issued coarse or fine adjustment power command. The voltage at the beginning of the parallel transmission circuit is multiplied by the voltage at the end of the parallel transmission circuit, divided by the reactance of the parallel transmission circuit, and then multiplied by the sine difference. This equals the coarse or fine adjustment power corresponding to the parallel transmission circuit. The sine difference is the sine value of the phase angle difference between the voltage at the beginning and end of the parallel transmission circuit after adjustment minus the sine value of the phase angle difference between the voltage at the beginning and end of the parallel transmission circuit before adjustment.

17. The control method for the COSCO Shipping New Energy Low-Frequency Gathering and Transmission Topology according to claim 12, characterized in that: The synchronous generator in the MG unit corresponding to the parallel output circuit of the control fault provides transient voltage and frequency support to the power grid or users, specifically as follows: For the excitation device of the synchronous generator in the corresponding MG unit, the excitation control technology of automatic voltage regulator (AVR) is adopted to improve the terminal voltage of the MG unit and provide voltage support on the grid-connected side. At the same time, the inertia support capability of the synchronous generator is used to slow down the frequency drop, and the speed governor of the synchronous generator adjusts the frequency according to the speed deviation, together providing frequency support on the grid-connected side.

18. The control method for the COSCO Shipping New Energy Low-Frequency Gathering and Transmission Topology according to claim 12, characterized in that: The power flow redistribution is specifically as follows: Power flow control of each parallel output circuit is performed by the energy routers on the N parallel output circuits (excluding those affected by the fault) through different modes.

19. An apparatus comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: The processor performs the steps of the control method using the COSCO Shipping New Energy low-frequency collection and transmission topology according to any one of claims 12 to 18.

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