CN115459333A - Flexible low-frequency alternating current sending-out system for offshore wind power and control method thereof - Google Patents
Flexible low-frequency alternating current sending-out system for offshore wind power and control method thereof Download PDFInfo
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- CN115459333A CN115459333A CN202211200676.6A CN202211200676A CN115459333A CN 115459333 A CN115459333 A CN 115459333A CN 202211200676 A CN202211200676 A CN 202211200676A CN 115459333 A CN115459333 A CN 115459333A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
- H02J2003/365—Reducing harmonics or oscillations in HVDC
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The invention discloses a flexible low-frequency alternating current sending system for offshore wind power and a control method thereof, wherein the system comprises: the offshore low-frequency alternating current power transmission platform adopts a low-frequency alternating current mode, and a back-to-back converter system is built on the onshore back-to-back bipolar direct current power transmission platform in a co-station manner, so that an offshore converter station is not required to be built, the investment cost is reduced, the volume and the cost of the offshore converter station are reduced, the operation loss is reduced, and the economy is improved.
Description
Technical Field
The invention relates to the technical field of offshore wind power transmission, in particular to a flexible low-frequency alternating current transmission system for offshore wind power and a control method thereof.
Background
When the scale of an offshore wind farm is small and the offshore is relatively close, a high-voltage power frequency alternating current is generally adopted to access an onshore power grid. Due to the influence of cable capacitance current, a high-voltage power frequency alternating current sending grid-connected mode cannot carry out long-distance transmission, so that a direct current transmission technology is mainly adopted at present for sending out a long-distance and large-capacity offshore wind farm. In recent years, flexible direct current transmission technology has been rapidly developed. Meanwhile, the output power of the wind power plant can be quickly and flexibly controlled by the flexible direct current, the bus voltage and the frequency of a grid-connected point of the wind power plant can be independently controlled, the power of the wind power plant is accessed by the flexible direct current and is transmitted to an onshore power grid, and the flexible direct current type wind power plant is applied to practical engineering at home and abroad at present. However, the existing offshore wind power is sent out of the offshore converter station through the flexible direct current and the existing onshore converter station both adopt the modular multilevel converter, and with the increase of the offshore wind power transmission scale, the size and the weight of the offshore platform converter station based on the modular multilevel converter are greatly increased, so that the construction difficulty and the construction cost of the project are greatly increased.
Some direct current transmission systems and control methods thereof in the prior art cannot avoid the construction of an offshore converter station and a submarine cable, and the construction, operation and maintenance costs of offshore wind power transmission are high, which becomes a bottleneck of large-scale offshore wind power development.
Disclosure of Invention
The invention provides a flexible low-frequency alternating current sending system for offshore wind power and a control method thereof, which can reduce the construction cost and the operation and maintenance cost of sending the offshore wind power while ensuring the stable sending of the offshore wind power.
In a first aspect, the invention provides a system for sending out offshore wind power through flexible low-frequency alternating current, comprising: the system comprises an offshore wind farm, an offshore low-frequency alternating-current power transmission platform and a land back-to-back bipolar direct-current power transmission platform connected with the offshore low-frequency alternating-current power transmission platform;
the offshore low-frequency alternating-current power transmission platform comprises: the offshore wind power station comprises an offshore booster station and an offshore low-frequency alternating-current cable which are sequentially connected, wherein the offshore booster station is connected with the offshore wind power plant;
the onshore back-to-back bipolar direct current transmission platform comprises: the system comprises a converter transformer, a wind field side pole 1MMC converter valve, a pole 2DR converter valve, a pole 1 direct current bus, a pole 2 direct current bus, a metal return bus, a power grid side pole 1MMC converter valve and a pole 2MMC converter valve; the wind field side pole 1MMC converter valve is connected with the pole 2MMC converter valve through the pole 1 direct current bus, the pole 2DR converter valve is connected with the power grid side pole 1MMC converter valve through the pole 2 direct current bus, the wind field side pole 1MMC converter valve is connected with the pole 2DR converter valve to form a first node, the power grid side pole 1MMC converter valve is connected with the pole 2MMC converter valve to form a second node, and the first node and the second node are connected through the metal return bus and then grounded; the wind field side pole 1MMC converter valve is connected with one offshore low-frequency alternating current cable through one converter transformer, the pole 2DR converter valve is connected with one offshore low-frequency alternating current cable through one converter transformer, and the power grid side pole 1MMC converter valve and the pole 2MMC converter valve are respectively connected with an onshore alternating current main network. .
Optionally, the converter transformer connected with the wind farm side pole 1MMC converter valve and the converter transformer connected with the pole 2DR converter valve are connected by an ac tie.
Optionally, both ends of the offshore low-frequency alternating-current cable are connected with offshore low-frequency circuit breakers.
Optionally, the power grid side pole 1MMC converter valve and the pole 2MMC converter valve both adopt a constant direct current voltage control mode to control the stable output of the direct current voltage of the corresponding pole.
Optionally, the wind field side pole 1MMC converter valve adopts a V/F control mode of a constant alternating current voltage amplitude and a constant alternating current system frequency to control the voltage and frequency of the offshore low-frequency alternating current power transmission platform to be stably output; and the wind field side pole 1MMC converter valve controls the alternating-current side voltage of the pole 2DR converter valve so as to control the conduction or the closing of the pole 2DR converter valve.
Optionally, the wind farm side pole 1MMC converter valve controls the frequency of the offshore low-frequency ac transmission platform to be a frequency value lower than 50 Hz.
Optionally, the voltage of the offshore low-frequency alternating-current transmission platform is controlled to be 220kV by the wind field side pole 1MMC converter valve.
In a second aspect, the present invention provides a control method for offshore wind power through a flexible low-frequency ac transmission system, which is applied to the offshore wind power through a flexible low-frequency ac transmission system as mentioned in the first aspect, and the method includes:
acquiring the total output power of the offshore wind power plant in the flexible low-frequency alternating current sending system and the transmission capacity of the pole 2DR converter valve;
and controlling the pole 2DR converter valve to transmit the total output power or controlling the wind field side pole 1MMC converter valve and the pole 2DR converter valve to jointly transmit the total output power according to the total output power and the transmission capacity.
Optionally, controlling the pole 2DR converter valve to transmit the total output power or controlling the wind farm side pole 1MMC converter valve and the pole 2DR converter valve to jointly transmit the total output power according to the total output power and the transmission capacity includes:
if the total output power is less than or equal to the transmission capacity, controlling the polar 2DR converter valve to transmit the total output power;
if the total output power is larger than the transmission capacity, controlling the pole 2DR converter valve to transmit transmission power according to the transmission capacity, and transmitting the residual transmission power through the wind field side pole 1MMC converter valve; wherein the remaining transmission power is a power difference between the total output power and the transmission capacity.
In a third aspect, the present invention provides a control device for an offshore wind power flexible low-frequency ac transmission system, which is applied to the offshore wind power flexible low-frequency ac transmission system mentioned in the first aspect, and the device includes:
the acquisition module is used for acquiring the total output power of the offshore wind power plant in the flexible low-frequency alternating current sending system and the transmission capacity of the pole 2DR converter valve;
and the control module is used for controlling the pole 2DR converter valve to transmit the total output power or controlling the wind field side pole 1MMC converter valve and the pole 2DR converter valve to jointly transmit the total output power according to the total output power and the transmission capacity.
According to the technical scheme, the invention has the following advantages:
the invention discloses a flexible low-frequency alternating current sending system for offshore wind power and a control method thereof, wherein the flexible low-frequency alternating current sending system comprises the following steps: the system comprises an offshore wind farm, an offshore low-frequency alternating-current power transmission platform and a land back-to-back bipolar direct-current power transmission platform connected with the offshore low-frequency alternating-current power transmission platform; the offshore low-frequency alternating-current power transmission platform comprises: the offshore booster station is connected with the offshore wind farm; the onshore back-to-back bipolar direct current transmission platform comprises: the system comprises a converter transformer, a wind field side pole 1MMC converter valve, a pole 2DR converter valve, a pole 1 direct current bus, a pole 2 direct current bus, a metal return bus, a power grid side pole 1MMC converter valve and a pole 2MMC converter valve; the wind field side pole 1MMC converter valve is connected with the pole 2MMC converter valve through the pole 1 direct current bus, the pole 2DR converter valve is connected with the power grid side pole 1MMC converter valve through the pole 2 direct current bus, the wind field side pole 1MMC converter valve is connected with the pole 2DR converter valve to form a first node, the power grid side pole 1MMC converter valve is connected with the pole 2MMC converter valve to form a second node, and the first node and the second node are connected through the metal return bus and then grounded; the wind field side pole 1MMC converter valve is connected with one offshore low-frequency alternating current cable through one converter transformer, the pole 2DR converter valve is connected with one offshore low-frequency alternating current cable through one converter transformer, and the power grid side pole 1MMC converter valve and the pole 2MMC converter valve are respectively connected with an onshore alternating current main network. The offshore low-frequency alternating current power transmission platform adopts a low-frequency alternating current mode, and a back-to-back converter system is built on the onshore back-to-back bipolar direct current power transmission platform in a co-station mode, so that an offshore converter station is not required to be built, the investment cost is reduced, the size and the cost of the offshore converter station are reduced, the operation loss is reduced, and the economy is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts;
FIG. 1 is a schematic circuit diagram of an embodiment of a system for transmitting offshore wind power via flexible low frequency AC transmission according to the present invention;
FIG. 2 is a flowchart illustrating steps of an embodiment of a method for controlling the flexible low frequency AC wind power transmission system of offshore wind power, according to the present invention;
fig. 3 is a block diagram of a control device of an embodiment of the flexible low-frequency ac transmission system for offshore wind power of the present invention.
In the figure: 1. an offshore wind farm; 2. an AC tie line; 3. an offshore booster station; 4. marine low frequency ac cables; 5. an offshore low frequency circuit breaker; 6. a converter transformer; 7. a wind field side pole 1MMC converter valve; 8. a pole 2DR converter valve; 9. a pole 1 dc bus; 10. a pole 2 dc bus; 11. a metal return bus; 12. a power grid side pole 1MMC converter valve; 13. a pole 2MMC converter valve; 14. exchanging a main network on land; 15. an offshore low-frequency alternating-current power transmission platform; 16. a land back-to-back bipolar direct current transmission platform.
Detailed Description
The embodiment of the application provides a system for sending out offshore wind power through flexible low-frequency alternating current and a control method thereof, which can reduce the construction cost and the operation and maintenance cost of sending out offshore wind power while ensuring the stable sending out of offshore wind power.
In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
For easy understanding, please refer to fig. 1, in which fig. 1 is a schematic circuit diagram of an embodiment of a flexible low-frequency ac transmission system for offshore wind power of the present invention, including: the system comprises an offshore wind farm 1, an offshore low-frequency alternating-current power transmission platform 15 and an onshore back-to-back bipolar direct-current power transmission platform 16 connected with the offshore low-frequency alternating-current power transmission platform 15;
the offshore low-frequency alternating-current power transmission platform 15 comprises: the offshore booster station 3 is connected with the offshore wind power plant 1;
the land-based back-to-back bipolar dc transmission platform 16 includes: the system comprises a converter transformer 6, a wind field side pole 1MMC converter valve 7, a pole 2DR converter valve 8, a pole 1 direct current bus 9, a pole 2 direct current bus 10, a metal return bus 11, a power grid side pole 1MMC converter valve 12 and a pole 2MMC converter valve 13; the wind field side pole 1MMC converter valve 7 is connected with the pole 2MMC converter valve 13 through the pole 1 direct current bus 9, the pole 2DR converter valve 8 is connected with the power grid side pole 1MMC converter valve 12 through the pole 2 direct current bus 10, the wind field side pole 1MMC converter valve 7 is connected with the pole 2DR converter valve 8 to form a first node, the power grid side pole 1MMC converter valve 12 is connected with the pole 2MMC converter valve 13 to form a second node, and the first node and the second node are connected through the metal return bus 11 and then grounded; wind field side utmost point 1MMC converter valve 7 is through one converter transformer 6 is connected with one marine low frequency alternating current cable 4, utmost point 2DR converter valve 8 is through one converter transformer 6 is connected with one marine low frequency alternating current cable 4, electric wire netting side utmost point 1MMC converter valve 12 with utmost point 2MMC converter valve 13 is connected with land interchange major network 14 respectively.
It should be noted that the MMC in the embodiment of the present invention is mainly in a 3-phase 6-leg form, and each leg is formed by mixing N full-half-bridge power modules. Wherein N is generally 10 or more.
Specifically, the converter transformer 6 connected with the wind field side pole 1MMC converter valve 7 and the converter transformer 6 connected with the pole 2DR converter valve 8 are connected through an alternating current tie 2.
Specifically, the two ends of the marine low-frequency alternating current cable 4 are connected with marine low-frequency circuit breakers 5.
In the embodiment of the invention, the wind field side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 are connected to form a first node, the grid side pole 1MMC converter valve 12 and the pole 2MMC converter valve 13 are connected to form a second node, the first node and the second node are connected through the metal return bus 11 and then grounded, and the direct currents of the two poles in the grounding mode can be unequal, so that the wind field side pole 1MMC converter valve 7 and the pole 2MMC converter valve 13, the grid side pole 1MMC converter valve 12 and the pole 2DR converter valve 8 respectively form a single-pole metal return wire capable of operating independently and share the metal return bus 11. In order to fix the ground point positions of the devices on the direct current side in the land back-to-back bipolar direct current transmission platform 16, the grounding grid corresponding to the metal return bus 11 is grounded, so that the bipolar unbalanced current can be prevented from flowing into the ground and the sea, the electrical corrosion problem caused by the current in the ground is also avoided, the influence on the environment is reduced, and the maintenance cost of the system is reduced.
In an alternative embodiment, the wind turbines in the offshore wind farm 1 are low frequency wind turbines. The total capacity of the low-frequency wind turbine generator set can be 2200MW, and correspondingly, the unipolar capacities of the onshore back-to-back bipolar direct-current power transmission platforms 16 are all 1000MW, and the bipolar capacity is 2000MW altogether.
In the above embodiment of the present invention, the offshore low-frequency ac power transmission platform 15 adopts a low-frequency ac mode, a back-to-back converter system is built on the onshore back-to-back bipolar dc power transmission platform 16 in a co-station manner, the ac-dc-ac frequency conversion is realized by adopting true bipolar dc power transmission, both the grid-side bipolar adopts an MMC scheme, both the wind farm-side bipolar adopts a mixed scheme of MMC and DR, the voltage and frequency of the offshore low-frequency ac power transmission platform 15 are established by the wind farm-side MMC, and the power generated by the offshore wind farm 1 is simultaneously transmitted by the dc-side MMC and DR. According to the embodiment of the invention, the back-to-back converter station is built only on land, and the offshore converter station is not required to be built, so that the investment cost is reduced, the size and the cost of the offshore converter station are reduced, the operation loss is reduced, and the economy is improved.
Specifically, the power grid side pole 1MMC converter valve 12 and the pole 2MMC converter valve 13 both adopt a constant direct current voltage control mode to control the stable output of the direct current voltage of the corresponding pole.
Specifically, the wind field side pole 1MMC converter valve 7 adopts a V/F control mode of a constant alternating current voltage amplitude and a constant alternating current system frequency to control the voltage and frequency of the offshore low-frequency alternating current power transmission platform 15 to be stably output; and the wind field side pole 1MMC converter valve 7 controls the alternating-current side voltage of the pole 2DR converter valve 8 so as to control the conduction or the closing of the pole 2DR converter valve 8.
In the embodiment of the invention, the voltage and the frequency of the offshore low-frequency alternating-current power transmission platform 15 can be controlled to be gradually increased to required values through a V/F control mode.
In a specific implementation, the alternating-current side voltage of the pole 2DR converter valve 8 is established by the wind field side pole 1MMC converter valve 7, and the pole 2DR converter valve 8 is conducted when the alternating-current side voltage is greater than a threshold value. Because the pole 1 and the pole 2 are connected through the bus, the voltage of the pole 2 alternating current side also rises, and then the pole 2DR converter valve 8 is conducted and started, so that the wind field side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 can jointly transmit the power of the offshore wind farm 1 to the onshore alternating current main grid 14.
Specifically, the wind field side pole 1MMC converter valve 7 controls the frequency of the offshore low-frequency alternating-current transmission platform 15 to be a frequency value lower than 50 Hz.
Specifically, the wind field side pole 1MMC converter valve 7 controls the voltage of the offshore low-frequency alternating-current transmission platform 15 to be 220kV.
In the embodiment of the invention, the frequency of the offshore low-frequency alternating current power transmission platform 15 is lower than 50Hz, so that the transmission distance of the offshore low-frequency alternating current cable 4 is increased, and the requirements of economic sending-out and high-efficiency collection of medium-distance and long-distance offshore wind power can be met.
As an embodiment, the wind farm side pole 1MMC converter valve 7 controls the frequency of the offshore low frequency ac transmission platform 15 at 20Hz. Due to the influence of the charging current of the cable to the ground capacitance, the transmission distance of the offshore low-frequency alternating current cable 4 is difficult to exceed 70 kilometers when the power frequency is 50 Hz. Because the frequency of the offshore low-frequency alternating current power transmission platform 15 is 20Hz which is greatly lower than the power frequency of 50Hz, the conveying distance of the offshore low-frequency alternating current cable 4 can be increased, and the conveying distance of the offshore low-frequency alternating current cable 4 can reach more than 70 km.
In the above embodiments of the present invention, the constant dc voltage control mode and the constant ac voltage amplitude and the constant ac system frequency V/F control mode are all the prior art, and are not described in detail herein. The voltage threshold corresponding to the ac side voltage of the pole 2DR converter valve 8 can be set according to the requirement, and is not limited herein.
The invention discloses a flexible low-frequency alternating current sending system for offshore wind power, which comprises: the system comprises an offshore wind farm 1, an offshore low-frequency alternating-current power transmission platform 15 and an onshore back-to-back bipolar direct-current power transmission platform 16 connected with the offshore low-frequency alternating-current power transmission platform 15; the offshore low-frequency alternating-current power transmission platform 15 comprises: the offshore booster station 3 is connected with the offshore wind power plant 1; the land-based back-to-back bipolar dc transmission platform 16 includes: the system comprises a converter transformer 6, a wind field side pole 1MMC converter valve 7, a pole 2DR converter valve 8, a pole 1 direct current bus 9, a pole 2 direct current bus 10, a metal return bus 11, a power grid side pole 1MMC converter valve 12 and a pole 2MMC converter valve 13; the wind field side pole 1MMC converter valve 7 is connected with the pole 2MMC converter valve 13 through the pole 1 direct current bus 9, the pole 2DR converter valve 8 is connected with the power grid side pole 1MMC converter valve 12 through the pole 2 direct current bus 10, the wind field side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 are connected to form a first node, the power grid side pole 1MMC converter valve 12 and the pole 2MMC converter valve 13 are connected to form a second node, and the first node and the second node are connected through the metal return bus 11 and then grounded; wind field side utmost point 1MMC converter valve 7 is through one converter transformer 6 is connected with one marine low frequency alternating current cable 4, utmost point 2DR converter valve 8 is through one converter transformer is with one marine low frequency alternating current cable 4 is connected, electric wire netting side utmost point 1MMC converter valve 12 with utmost point 2MMC converter valve 13 is connected with land interchange major network 14 respectively. The offshore low-frequency alternating current power transmission platform 15 adopts a low-frequency alternating current mode, a back-to-back converter system is built on the onshore back-to-back bipolar direct current power transmission platform 16 in a co-station mode, an offshore converter station is not required to be built, the investment cost is reduced, the size and the cost of the offshore converter station are reduced, the operation loss is reduced, and the economical efficiency is improved.
Referring to fig. 2, fig. 2 is a flowchart illustrating steps of an embodiment of a method for controlling the flexible low-frequency ac transmission system of the offshore wind power, which is applied to the flexible low-frequency ac transmission system of the offshore wind power, and includes:
step S101, acquiring the total output power of the offshore wind power plant 1 and the transmission capacity of the pole 2DR converter valve 8 in the flexible low-frequency alternating current sending system of the offshore wind power;
and S102, controlling the pole 2DR converter valve 8 to transmit the total output power or controlling the wind field side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 to jointly transmit the total output power according to the total output power and the transmission capacity.
In an alternative embodiment, controlling the pole 2DR converter valve 8 to deliver the total output power or controlling the wind farm side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 to jointly deliver the total output power according to the total output power and the delivery capacity comprises:
if the total output power is less than or equal to the delivery capacity, controlling the polar 2DR converter valve 8 to deliver the total output power;
if the total output power is larger than the transmission capacity, controlling the pole 2DR converter valve 8 to transmit transmission power according to the transmission capacity, and transmitting the residual transmission power through the wind field side pole 1MMC converter valve 7; wherein the remaining transmission power is a power difference between the total output power and the transmission capacity.
It should be noted that whether the pole 1MMC converter valve 7 and the pole 2DR converter valve 8 on the wind farm side transmit the total output power to the onshore alternating-current main network 14 or not is mainly controlled according to the total output power and the transmission capacity, so that the running loss of the onshore back-to-back bipolar direct-current transmission platform 16 is reduced, and the feasibility and the stability of the long-term running of the offshore wind power through the flexible low-frequency alternating-current transmission system are improved.
In the embodiment of the invention, when the total output power is not more than the transmission capacity, the pole 2DR converter valve 8 takes on the transmission power transmission task; and when the total output power is not more than the transmission capacity, the wind field side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 jointly transmit the total output power.
The invention discloses a control method of an offshore wind power flexible low-frequency alternating current sending system, which comprises the steps of obtaining the total output power of an offshore wind farm 1 and the transmission capacity of a polar 2DR converter valve 8 in the offshore wind power flexible low-frequency alternating current sending system; and controlling the pole 2DR converter valve 8 to transmit the total output power or controlling the wind field side pole 1MMC converter valve 7 and the pole 2DR converter valve 8 to jointly transmit the total output power according to the total output power and the transmission capacity. Therefore, under the condition of ensuring that offshore wind power is stably sent out, the investment cost is reduced, the size and the cost of the offshore converter station are reduced, and the operation loss is reduced.
Referring to fig. 3, fig. 3 is a block diagram of a control device of an embodiment of the present invention, which is applied to the above-mentioned system for sending out offshore wind power via flexible low-frequency ac, and the device includes:
an obtaining module 301, configured to obtain total output power of the offshore wind power plant and a transmission capacity of the polar 2DR converter valve in the system through flexible low-frequency ac transmission;
and the control module 302 is configured to control the pole 2DR converter valve to transmit the total output power according to the total output power and the transmission capacity, or control the wind farm side pole 1MMC converter valve and the pole 2DR converter valve to transmit the total output power together.
In an alternative embodiment, the control module 302 includes:
a first control sub-module for controlling the pole 2DR converter valve to deliver the total output power when the total output power is less than or equal to the delivery capacity;
the second control submodule is used for controlling the pole 2DR converter valve to transmit transmission power according to the transmission capacity when the total output power is larger than the transmission capacity, and transmitting the residual transmission power through the wind field side pole 1MMC converter valve; wherein the remaining transmission power is a power difference between the total output power and the transmission capacity.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working process of the apparatus described above may refer to the corresponding process in the foregoing method embodiment, and is not described herein again.
In the embodiments provided in the present invention, it should be understood that the disclosed apparatus and method can be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one type of logical functional division, and other divisions may be realized in practice, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed coupling or direct coupling or communication connection between each other may be through some interfaces, profiles of devices or units or communication connection, and may be electrical, mechanical or other forms.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit may be implemented in the form of hardware, or may also be implemented in the form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A system for transmitting offshore wind power through flexible low-frequency alternating current is characterized by comprising: the system comprises an offshore wind farm, an offshore low-frequency alternating-current power transmission platform and a land back-to-back bipolar direct-current power transmission platform connected with the offshore low-frequency alternating-current power transmission platform;
the offshore low-frequency alternating-current power transmission platform comprises: the offshore booster station is connected with the offshore wind farm;
the onshore back-to-back bipolar direct current transmission platform comprises: the system comprises a converter transformer, a wind field side pole 1MMC converter valve, a pole 2DR converter valve, a pole 1 direct current bus, a pole 2 direct current bus, a metal return bus, a power grid side pole 1MMC converter valve and a pole 2MMC converter valve; the wind field side pole 1MMC converter valve is connected with the pole 2MMC converter valve through the pole 1 direct current bus, the pole 2DR converter valve is connected with the power grid side pole 1MMC converter valve through the pole 2 direct current bus, the wind field side pole 1MMC converter valve is connected with the pole 2DR converter valve to form a first node, the power grid side pole 1MMC converter valve is connected with the pole 2MMC converter valve to form a second node, and the first node and the second node are connected through the metal return bus and then grounded; the wind field side pole 1MMC converter valve is connected with one offshore low-frequency alternating current cable through one converter transformer, the pole 2DR converter valve is connected with one offshore low-frequency alternating current cable through one converter transformer, and the power grid side pole 1MMC converter valve and the pole 2MMC converter valve are respectively connected with an onshore alternating current main network.
2. The offshore wind power flexible low-frequency alternating current transmission system according to claim 1, wherein the converter transformer connected with the wind farm side pole 1MMC converter valve and the converter transformer connected with the pole 2DR converter valve are connected through an alternating current connecting line.
3. The offshore wind power flexible low-frequency alternating current transmission system according to claim 1, wherein both ends of the offshore low-frequency alternating current cable are connected with an offshore low-frequency circuit breaker.
4. The offshore wind power flexible low-frequency alternating-current transmission system according to claim 1, wherein the grid side pole 1MMC converter valve and the pole 2MMC converter valve both adopt a constant direct-current voltage control mode to control the stable output of direct-current voltage of corresponding poles.
5. The offshore wind power flexible low-frequency alternating current transmission system according to claim 1, wherein the wind farm side pole 1MMC converter valve controls the voltage and frequency stability output of the offshore low-frequency alternating current transmission platform in a V/F control mode of constant alternating current voltage amplitude and constant alternating current system frequency; and the wind field side pole 1MMC converter valve controls the alternating-current side voltage of the pole 2DR converter valve so as to control the conduction or the closing of the pole 2DR converter valve.
6. The offshore wind power flexible low-frequency alternating current transmission system according to claim 5, wherein the wind farm side pole 1MMC converter valve controls the frequency of the offshore low-frequency alternating current transmission platform to a frequency value below 50 Hz.
7. The offshore wind power flexible low-frequency alternating current transmission system according to claim 5, wherein the wind farm side pole 1MMC converter valve controls the voltage of the offshore low-frequency alternating current transmission platform to be 220kV.
8. A control method of an offshore wind power flexible low-frequency alternating current sending system, which is applied to the offshore wind power flexible low-frequency alternating current sending system of any one of claims 1 to 7, and comprises the following steps:
acquiring the total output power of the offshore wind power through the flexible low-frequency alternating current sending system to the offshore wind power plant and the transmission capacity of the pole 2DR converter valve;
and controlling the pole 2DR converter valve to transmit the total output power or controlling the wind field side pole 1MMC converter valve and the pole 2DR converter valve to jointly transmit the total output power according to the total output power and the transmission capacity.
9. The method for controlling offshore wind power through a flexible low-frequency alternating current transmission system according to claim 8, wherein controlling the pole 2DR converter valve to transmit the total output power or controlling the wind farm side pole 1MMC converter valve and the pole 2DR converter valve to jointly transmit the total output power according to the total output power and the transmission capacity comprises:
if the total output power is less than or equal to the transmission capacity, controlling the polar 2DR converter valve to transmit the total output power;
if the total output power is larger than the transmission capacity, controlling the pole 2DR converter valve to transmit transmission power according to the transmission capacity, and transmitting the residual transmission power through the wind field side pole 1MMC converter valve; wherein the remaining transmission power is a power difference between the total output power and the transmission capacity.
10. A control device for an offshore wind power flexible low-frequency alternating current delivery system, which is applied to the offshore wind power flexible low-frequency alternating current delivery system as claimed in any one of claims 1 to 7, and comprises:
the acquisition module is used for acquiring the total output power of the offshore wind power plant in the flexible low-frequency alternating current sending system and the transmission capacity of the pole 2DR converter valve;
and the control module is used for controlling the pole 2DR converter valve to transmit the total output power or controlling the wind field side pole 1MMC converter valve and the pole 2DR converter valve to jointly transmit the total output power according to the total output power and the transmission capacity.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211200676.6A CN115459333A (en) | 2022-09-29 | 2022-09-29 | Flexible low-frequency alternating current sending-out system for offshore wind power and control method thereof |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211200676.6A CN115459333A (en) | 2022-09-29 | 2022-09-29 | Flexible low-frequency alternating current sending-out system for offshore wind power and control method thereof |
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| CN115459333A true CN115459333A (en) | 2022-12-09 |
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| CN202211200676.6A Pending CN115459333A (en) | 2022-09-29 | 2022-09-29 | Flexible low-frequency alternating current sending-out system for offshore wind power and control method thereof |
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| Country | Link |
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| CN (1) | CN115459333A (en) |
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