Energy storage system for offshore wind power full DC collection and transmission with DC dynamic unloading

Abstract

The present invention proposes an energy storage system for offshore wind power full DC aggregation and DC dynamic unloading. Based on new energy storage and modular multi-level technology, the DC energy storage system is connected between DC buses. By controlling the switching of energy storage sub-modules, flexible control of charging / discharging current and DC voltage can be achieved; the battery's short-term high-rate charging capability is fully utilized to fully absorb surplus power when the main grid AC side fails, and the traditional high-cost and complex protection and coordination unloading energy-consuming devices can be eliminated; the technical solution of the present invention can accurately control the unloading power, avoid the power fluctuation problem caused by the frequent switching of traditional unloading resistors, and absorb the surplus power of wind power through energy storage to achieve energy recovery and utilization; the present invention innovatively uses a new energy storage system for transient unloading, which can realize the multifunctionality of the energy storage system and has high practical value and economic benefits.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to an energy storage system for offshore wind power full DC collection and DC dynamic unloading. Background Art

[0002] The full DC grid connection of offshore wind power has become an important technological development direction, with two major advantages: economic and technical. On the one hand, it can significantly reduce the manufacturing and installation costs of offshore platforms and improve the technical economy of grid connection. On the other hand, it can improve the stability and reliability of offshore wind turbines and converter stations, ensuring the safe and stable operation of the grid-connected system and even the AC main grid.

[0003] In an all-DC offshore wind power system, when a fault occurs in the onshore AC grid, the voltage drop at the connection point significantly reduces the power delivery capacity of the receiving converter, effectively blocking the wind power transmission path. If the voltage drop at the connection point is too severe, the wind power output will exceed the delivery capacity of the receiving converter station. This excess wind power will accumulate in the DC line. If this excess power cannot be promptly processed, the DC voltage will rise rapidly, triggering protective action at the flexible DC converter station, which can seriously impact the stable operation of the entire DC system. To address this excess power absorption in wind farms, two common solutions exist: AC load shedding and DC load shedding. AC load shedding can only be installed on the AC side of the sending end and is not suitable for all-DC offshore wind farms. DC load shedding is generally used. Current DC load shedding devices often consist of energy-dissipating resistors connected in series with switching devices, resulting in high construction costs and limited functionality. Summary of the Invention

[0004] The present invention proposes an energy storage system for offshore wind power full DC aggregation and DC dynamic unloading. Based on new energy storage and modular multi-level technology, its DC energy storage system is connected between DC buses. By controlling the switching of energy storage sub-modules, flexible control of charging / discharging current and DC voltage can be achieved.

[0005] The present invention adopts the following technical solutions.

[0006] An energy storage system for dynamic DC unloading of all-DC offshore wind power transmission, used in a grid-connected project for all-DC offshore wind power transmission. The grid-connected project includes a DC wind turbine, an offshore step-up transformer, a DC transmission cable, and an onshore converter station. The DC lines at the outlets of the DC wind turbines are connected to the offshore DC step-up transformer, and the DC step-up transformer output is transmitted to the onshore converter station in a DC manner. The onshore converter station converts the DC power into AC power to achieve grid connection with the main grid. The energy storage system is connected to the positive and negative busbars of the DC system transmission cable of the project, and includes a series-connected energy storage converter valve section, a current-limiting reactor, a starting resistor, and a DC fast switch.

[0007] The current limiting reactor is used to limit the closing current of the energy storage system connected to the busbar;

[0008] The starting resistor and the DC fast switch are used to put the energy storage system online and offline without affecting the normal operation of the DC system;

[0009] The energy storage type converter valve section includes N energy storage type submodules, where N is a natural number greater than or equal to 2, and the energy storage type submodule includes a power unit, a DC capacitor, a bypass circuit, a filter inductor, a battery module and a control module;

[0010] The power unit is composed of a power semiconductor device and a drive circuit thereof;

[0011] The power unit includes an AC side and a DC side. The DC side positive electrode is sequentially connected in series with a bypass circuit, a filter inductor, and a battery module to the DC side negative electrode. The DC capacitor is connected in parallel to the two DC side electrodes of the power unit. The energy storage submodule is sequentially connected in series on the AC side of the power unit.

[0012] The energy storage system controls the charging / discharging current and DC voltage of the energy storage system by controlling the switching of energy storage sub-modules; and uses the short-term high-rate charging condition of the battery modules to fully absorb the surplus power in the event of a fault on the AC side of the main grid.

[0013] The energy storage submodule includes an energy-taking power supply connected to a DC capacitor and / or the battery module, which is used to power the power unit and battery control unit of the energy storage submodule in which it is located. The number of energy-taking power supplies is one or more.

[0014] The power unit is a two-level or three-level circuit composed of power semiconductor devices, and adopts a full-bridge circuit, a half-bridge circuit or a full-bridge and half-bridge hybrid circuit.

[0015] The bypass circuit is formed by connecting a switch and a pre-charging resistor in parallel, and the battery module is formed by connecting battery cells in series and in parallel.

[0016] Online startup refers to putting the energy storage system into operation during the normal operation of the DC system; online shutdown refers to shutting down the energy storage system without affecting the normal operation of the DC system and reducing the impact on the DC system during the startup process.

[0017] The energy storage system further includes an energy storage control module, a power control module, and a valve control unit communicating with the energy storage submodule; the energy storage control module communicates with the power control module in an optical communication manner or an electrical signal communication manner;

[0018] The energy storage control module receives control instructions from the valve control unit and / or the power control module;

[0019] The power control module receives control instructions from the valve control unit and / or the energy storage control module.

[0020] The parameter setting method of the energy storage system comprises the following steps:

[0021] Step S1: Determine the transient power P that the energy storage system can absorb 储 ; Determine the minimum number N of the energy storage submodules min ; Determine the number M of parallel branches of battery modules;

[0022] Step S2: Assume that the wind farm voltage u 风 Down to 0.9U N After the following, the wind turbine will start low voltage ride through, and output reactive current according to the following:

[0023]

[0024] Where: U N is the rated voltage of the wind farm; I N is the rated current;

[0025] Step S3: According to the maximum value formula of active current: Get i lim is the maximum output current of the wind farm; the active power limit P of the wind farm is obtained max =u 风 ×i d,max , determine the transient absorbed power P of the energy storage system 储 , so that P 储 ≥P max ;

[0026] Step S4: Based on the DC access point voltage U of the new energy storage system and the semiconductor device withstand voltage level U of the power unit 功率模块 , determine the minimum number N of the energy storage submodules min , making U 功率模块 ×N min ≥U; Step S5, according to the transient absorption power P of the energy storage system 储 and the DC access point voltage U to determine the unloading current I that the energy storage system can withstand transiently 卸荷 , so that U×I 卸荷 ≥P 储 ;

[0027] Step S6: Based on the cell specification A of the battery module and the transient charge and discharge capability value A 暂态 , calculate the number of parallel branches of battery modules M, so that M×A 暂态 ≥I 卸荷 ;

[0028] Step S7: Select N = (1 + k) × Nmin , k is the redundancy coefficient of the energy storage submodule.

[0029] Calculate the total energy storage capacity C = N × battery module capacity C i ;

[0030] The total capacity C≥W, where W is the transient surplus wind energy that the energy storage needs to absorb.

[0031] This invention leverages the energy storage system's capabilities to smooth wind power output fluctuations, actively support the grid, and provide fault ride-through, while also providing transient load shedding. This eliminates the need for traditional, costly, and complex load shedding devices. By absorbing excess wind power through energy storage, the energy storage system achieves multifunctionality and enables energy recovery, resulting in high practical value and economic benefits.

[0032] Compared with the existing technology, the present invention provides a new energy storage system and parameter design method for dynamic DC unloading of all-DC offshore wind power. The new energy storage system is based on new energy storage and modular multi-level technology. The DC energy storage system is connected between the DC busbars. By controlling the switching of energy storage submodules, flexible control of the charging / discharging current and DC voltage can be achieved.

[0033] The present invention can fully utilize the short-term high-rate charging capability of the battery, fully absorb the surplus power when a fault occurs on the AC side of the main grid, and eliminate the need for traditional high-cost and complex protection unloading energy-consuming devices.

[0034] The technical solution of the present invention can accurately control the unloading power, avoid the power fluctuation problem caused by the frequent switching of traditional unloading resistors, and absorb the surplus power of wind power through energy storage to achieve energy recovery and utilization.

[0035] The present invention applies energy storage to offshore wind power, and while playing the role of smoothing wind power output fluctuations, actively supporting the power grid, and riding through faults, it innovatively adopts a new energy storage system for transient unloading, realizing the multifunctionality of the energy storage system, which has high practical value and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0037] Attachment Figure 1 This is a schematic diagram of the offshore wind power all-DC transmission and grid-connected project connected to the energy storage system of the present invention;

[0038] Attachment Figure 2 It is a schematic structural diagram of the energy storage system of the present invention;

[0039] Attachment Figure 3 is a detailed structural diagram of the energy storage system of the present invention;

[0040] Attachment Figure 4 This is a topological diagram of the energy storage submodule based on a half-bridge circuit;

[0041] Attachment Figure 5 This is a topological diagram of the energy storage submodule based on a full-bridge circuit. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0043] The embodiment of the present application is based on an offshore wind power full DC collection and transmission grid-connected system, and is a multi-voltage level offshore wind power DC grid-connected technology based on DC collection and DC transmission.

[0044] Energy storage system used for offshore wind power full DC transmission and DC dynamic unloading, used for offshore wind power full DC transmission and grid connection project, such as Figure 1 As shown, the grid-connected project includes a DC wind turbine, an offshore boost transformer, a DC transmission cable, and an onshore converter station. The DC lines at the outlet of the DC wind turbine are connected to the offshore DC boost transformer. The DC boost transformer output is transmitted to the onshore converter station in a DC manner. The onshore converter station converts the DC power into AC power to achieve grid connection with the main grid. The energy storage system is connected to the positive and negative busbars of the DC system transmission cable of the project, as shown in FIG. Figure 2 As shown, it includes a series-connected energy storage type converter valve section, a current limiting reactor, a starting resistor and a DC fast switch;

[0045] The current limiting reactor is used to limit the closing current of the energy storage system connected to the busbar;

[0046] The starting resistor and the DC fast switch are used to put the energy storage system online and offline without affecting the normal operation of the DC system;

[0047] The energy storage type converter valve section includes N energy storage type submodules, where N is a natural number greater than or equal to 2, and the energy storage type submodule includes a power unit, a DC capacitor, a bypass circuit, a filter inductor, a battery module and a control module;

[0048] The power unit is composed of a power semiconductor device and a drive circuit thereof;

[0049] The power unit includes an AC side and a DC side. The DC side positive electrode is sequentially connected in series with a bypass circuit, a filter inductor, and a battery module to the DC side negative electrode. The DC capacitor is connected in parallel to the two DC side electrodes of the power unit. The energy storage submodule is sequentially connected in series on the AC side of the power unit.

[0050] The energy storage system controls the charging / discharging current and DC voltage of the energy storage system by controlling the switching of energy storage sub-modules; and uses the short-term high-rate charging condition of the battery modules to fully absorb the surplus power in the event of a fault on the AC side of the main grid.

[0051] The energy storage submodule includes an energy-taking power supply connected to a DC capacitor and / or the battery module, which is used to power the power unit and battery control unit of the energy storage submodule in which it is located. The number of energy-taking power supplies is one or more.

[0052] like Figure 4 、 Figure 5 As shown, the power unit is a two-level or three-level circuit composed of power semiconductor devices, and adopts a full-bridge circuit, a half-bridge circuit or a full-bridge and half-bridge hybrid circuit.

[0053] The bypass circuit is formed by connecting a switch and a pre-charging resistor in parallel, and the battery module is formed by connecting battery cells in series and in parallel.

[0054] Online startup refers to putting the energy storage system into operation during the normal operation of the DC system; online shutdown refers to shutting down the energy storage system without affecting the normal operation of the DC system and reducing the impact on the DC system during the startup process.

[0055] The energy storage system further includes an energy storage control module, a power control module, and a valve control unit communicating with the energy storage submodule; the energy storage control module communicates with the power control module in an optical communication manner or an electrical signal communication manner;

[0056] The energy storage control module receives control instructions from the valve control unit and / or the power control module;

[0057] The power control module receives control instructions from the valve control unit and / or the energy storage control module.

[0058] The parameter setting method of the energy storage system comprises the following steps:

[0059] Step S1: Determine the transient power P that the energy storage system can absorb 储 ; Determine the minimum number N of the energy storage submodules min ; Determine the number M of parallel branches of battery modules;

[0060] Step S2: Assume that the wind farm voltage u 风 Down to 0.9U NAfter the following, the wind turbine will start low voltage ride through, and output reactive current according to the following:

[0061]

[0062] Where: U N is the rated voltage of the wind farm; I N is the rated current;

[0063] Step S3: According to the maximum value formula of active current: Get i lim is the maximum output current of the wind farm; the active power limit P of the wind farm is obtained max =u 风 ×i d,max , determine the transient absorbed power P of the energy storage system 储 , so that P 储 ≥P max ;

[0064] Step S4: Based on the DC access point voltage U of the new energy storage system and the semiconductor device withstand voltage level U of the power unit 功率模块 , determine the minimum number N of the energy storage submodules min , making U 功率模块 ×N min ≥U; Step S5, according to the transient absorption power P of the energy storage system 储 and the DC access point voltage U to determine the unloading current I that the energy storage system can withstand transiently 卸荷 , so that U×I 卸荷 ≥P 储 ;

[0065] Step S6: Based on the cell specification A of the battery module and the transient charge and discharge capability value A 暂态 , calculate the number of parallel branches of battery modules M, so that M×A 暂态 ≥I 卸荷 ;

[0066] Step S7: Select N = (1 + k) × N min , k is the redundancy coefficient of the energy storage submodule.

[0067] Calculate the total energy storage capacity C = N × battery module capacity C i ;

[0068] The total capacity C≥W, where W is the transient surplus wind energy that the energy storage needs to absorb.

[0069] In this example, the main grid is the AC mains grid.

[0070] In this example, online investment means online input, and online switching means online exit.

[0071] The above is a detailed introduction to a new energy storage system and parameter design method for offshore wind power full DC collection and transmission dynamic unloading provided by the embodiment of the present application, and the principles and implementation methods of the present application are explained. The description of the above embodiments is only used to help understand the technical solution and core idea of ​​the present application; ordinary technicians in this field should understand that: they can still modify the technical solutions recorded in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. An energy storage system for offshore wind power generation with full DC converging and DC dynamic unloading, characterized by: The energy storage system is connected to the busbars of the positive and negative poles of the DC system transmission cable of the project, and includes an energy storage type converter valve section, a current limiting reactor, a starting resistor and a DC fast switch connected in series; The current limiting reactor is used to limit the closing current of the energy storage system connected to the busbar; The starting resistor and the DC fast switch are used to put the energy storage system online and offline without affecting the normal operation of the DC system; The energy storage type converter valve section includes N energy storage type submodules, where N is a natural number greater than or equal to 2, and the energy storage type submodule includes a power unit, a DC capacitor, a bypass circuit, a filter inductor, a battery module and a control module; The power unit is composed of a power semiconductor device and a drive circuit thereof; The power unit includes an AC side and a DC side. The DC side positive electrode is sequentially connected in series with a bypass circuit, a filter inductor, and a battery module to the DC side negative electrode. The DC capacitor is connected in parallel to the two DC side electrodes of the power unit. The energy storage submodule is sequentially connected in series on the AC side of the power unit. The parameter setting method of the energy storage system comprises the following steps: Step S1: Determine the transient power P that the energy storage system can absorb 储 ; Determine the minimum number N of the energy storage submodules min ; Determine the number M of parallel branches of battery modules; Step S2: Assume that the wind farm voltage u 风 Down to 0.9U N After the following, the wind turbine will start low voltage ride through, and output reactive current according to the following: Where: U N is the rated voltage of the wind farm; I N is the rated current; Step S3: Maximum value formula of active current: i lim Output the maximum current for the wind farm; Active power limit P of wind farm max =u 风 ×i d,max , determine the transient absorbed power P of the energy storage system 储 , so that P 储 ≥P max ; Step S4: Based on the DC access point voltage U of the energy storage system and the semiconductor device withstand voltage level U of the power unit 功率模块 , determine the minimum number N of the energy storage submodules min , making U 功率模块 ×N min ≥U; Step S5: According to the transient absorbed power P of the energy storage system 储 and the DC access point voltage U to determine the unloading current I that the energy storage system can withstand transiently 卸荷 , so that U×I 卸荷 ≥P 储 ; Step S6: Based on the cell specification A of the battery module and the transient charge and discharge capability value A 暂态 , calculate the number of parallel branches of battery modules M, so that M×A 暂态 ≥I 卸荷 ; Step S7: Select N = (1 + k) × N min , k is the redundancy coefficient of the energy storage submodule; Calculate the total energy storage capacity C = N × battery module capacity C i ; The total capacity C≥W, where W is the transient surplus wind energy that the energy storage needs to absorb.

2. The energy storage system for offshore wind power full DC aggregation and DC dynamic unloading according to claim 1 is characterized by: The energy storage submodule includes an energy-taking power supply connected to a DC capacitor and / or the battery module, which is used to power the power unit and battery control unit of the energy storage submodule in which it is located, and the number of energy-taking power supplies is more than one.

3. The energy storage system for offshore wind power full DC collection and DC dynamic unloading according to claim 1 is characterized by: The power unit is a two-level or three-level circuit composed of power semiconductor devices, and adopts a full-bridge circuit, a half-bridge circuit or a full-bridge and half-bridge hybrid circuit.

4. The energy storage system for offshore wind power full DC collection and DC dynamic unloading according to claim 1 is characterized by: The bypass circuit is formed by connecting a switch and a pre-charging resistor in parallel, and the battery module is formed by connecting battery cells in series and in parallel.

5. The energy storage system for offshore wind power full DC collection and DC dynamic unloading according to claim 1 is characterized by: Online startup refers to putting the energy storage system into operation during the normal operation of the DC system; online shutdown refers to shutting down the energy storage system without affecting the normal operation of the DC system and reducing the impact on the DC system during the startup process.

6. The energy storage system for offshore wind power full DC collection and DC dynamic unloading according to claim 1 is characterized by: The energy storage system further includes an energy storage control module, a power control module, and a valve control unit communicating with the energy storage submodule; the energy storage control module communicates with the power control module in an optical communication manner or an electrical signal communication manner; The energy storage control module receives control instructions from the valve control unit and / or the power control module; The power control module receives control instructions from the valve control unit and / or the energy storage control module.

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