CN106936154B - Series-parallel direct-current power grid starting method for large-scale long-distance offshore wind power grid connection - Google Patents

Series-parallel direct-current power grid starting method for large-scale long-distance offshore wind power grid connection Download PDF

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CN106936154B
CN106936154B CN201511019298.1A CN201511019298A CN106936154B CN 106936154 B CN106936154 B CN 106936154B CN 201511019298 A CN201511019298 A CN 201511019298A CN 106936154 B CN106936154 B CN 106936154B
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converter
vsc
voltage
lcc
power grid
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CN106936154A (en
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吴广禄
王峰
李亚楼
李蒙
安宁
陈绪江
王艺璇
彭红英
穆清
孙丽香
王祥旭
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
State Grid Jiangsu Electric Power Co Ltd
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
State Grid Jiangsu Electric Power Co Ltd
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    • H02J3/386—
    • 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
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • 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]

Abstract

The invention provides a method for starting a series-parallel direct-current power grid for large-scale long-distance offshore wind power grid connection, which comprises the following steps of 1: controlling the LCC converter to charge the VSC converter; step 2: wind generating sets are merged into the offshore wind farm one by one; and step 3: and after the LCC converter is controlled to work in an inversion state, the LCC converter and the VSC converter are operated in parallel. Compared with the prior art, the method for starting the series-parallel direct-current power grid for large-scale long-distance offshore wind power grid connection is simple and easy to implement, good in economy and free of a small alternating-current starting power supply on the long-distance offshore wind power plant side.

Description

Series-parallel direct-current power grid starting method for large-scale long-distance offshore wind power grid connection
Technical Field
The invention relates to the technical field of direct current transmission, in particular to a series-parallel direct current power grid starting method for large-scale long-distance offshore wind power grid connection.
Background
At present, LCC-HVDC is widely applied to occasions of submarine cable power transmission, large-capacity long-distance power transmission, asynchronous grid back-to-back interconnection and the like, but the defects that an inverter station possibly has phase change failure, cannot supply power to a weak alternating current system, needs to consume a large amount of reactive power in the operation process and the like exist, and further development of the LCC-HVDC is restricted. The voltage source converter high voltage direct current transmission (VSC-HVDC) based on the full-control power electronic device has the advantages of independently controlling active and reactive power, avoiding commutation failure, supplying power for a passive island and the like, but the system is expensive in manufacturing cost and cannot effectively process direct current faults. In order to be able to make reasonable use of the advantages of LCC-HVDC and VSC-HVDC systems, a series-parallel direct current transmission system is proposed, one end of which uses LCC and one end of which uses VSC, as shown in fig. 1. The series-parallel direct-current transmission system with the rectification side adopting VSC and the inversion side adopting LCC is suitable for large-scale long-distance offshore wind power grid connection. Before the hybrid direct-current transmission system enters steady-state operation, a starting control process is needed to charge a capacitor of a rectification side VSC converter, and in order to prevent overvoltage and overcurrent generated in the starting process from damaging the safety of a converter device, a reasonable starting control strategy must be designed for the starting process.
Because an offshore wind farm generally has no other power supplies except wind power, at present, a method for setting a small alternating current starting power supply (such as a diesel generator) on the wind farm side is mainly adopted for providing stable rectifying side alternating current voltage for a starting method of a series-parallel direct current power grid for large-scale long-distance offshore wind power grid connection, the starting of a rectifying side VSC converter is assisted, and the small alternating current starting power supply is withdrawn after a starting process is completed and a system enters stable operation. However, this method is expensive to construct and maintain.
Therefore, it is necessary to provide a large-scale long-distance offshore wind power grid-connected parallel-serial direct current power grid starting method which is simple and easy to implement, has good economy, and does not need a small alternating current starting power supply on the long-distance offshore wind farm side.
Disclosure of Invention
In order to meet the requirements of the prior art, the invention provides a series-parallel direct-current power grid starting method for large-scale long-distance offshore wind power grid connection.
The technical scheme of the invention is as follows:
the series-parallel direct-current power grid comprises a VSC converter and an LCC converter; the VSC converter is connected to an offshore wind power plant, the LCC converter is connected to a land alternating current system, the VSC converter and the LCC converter are connected through a submarine direct current cable, and the method comprises the following steps:
step 1: controlling the LCC converter to charge the VSC converter;
step 2: wind generating sets are merged into the offshore wind farm one by one;
and step 3: and after the LCC converter is controlled to work in an inversion state, the LCC converter and the VSC converter are operated in parallel.
Preferably, the step 1 of charging the VSC converter by the LCC converter includes a lockout charging mode and a semi-lockout charging mode.
Preferably, the lockout charging mode:
step 111: controlling the LCC converter to work in a rectification state, and closing circuit breakers at two ends of the submarine direct current cable;
step 112: controlling a voltage command V of the LCC converterdc1refSlowly increasing linearly from 0;
step 113: the direct current output by the LCC converter charges a capacitor through a diode of a submodule in the VSC converter;
when the locking charging mode is finished, the capacitor voltage of each submodule is
Figure BDA0000894765270000021
Wherein, Vdc1NTo a rated value of DC voltage, NsmThe number of the sub-modules contained in each phase of bridge arm in the VSC converter is equal to the number of the sub-modules contained in each phase of bridge arm in the VSC converter.
Preferably, the semi-latched charging mode is:
step 121: calculating the number n of sub-modules required to be input in the VSC converter,
Figure BDA0000894765270000022
wherein VmIs the ac side line voltage peak.
Step 122: carrying out capacitance voltage-sharing control on the VSC for ensuring the continuous charging of the capacitance of a sub-module of the VSC;
when the semi-locking charging mode is finished, the capacitor voltage of each submodule is
Figure BDA0000894765270000023
Wherein, Vdc1NTo a rated value of DC voltage, NsmThe number of the sub-modules contained in each phase of bridge arm in the VSC converter is equal to the number of the sub-modules contained in each phase of bridge arm in the VSC converter.
Preferably, a stator winding of the wind generating set in the step 2 is connected to a wind power plant output transformer through a first circuit breaker, and a rotor winding is connected to the wind power plant output transformer through a third circuit breaker, a rotor side converter, a grid side converter and a second circuit breaker in sequence; and the wind power plant output transformer is connected with the VSC converter through a fourth circuit breaker.
Preferably, in step 2, the wind generating sets are incorporated into the offshore wind farm one by one:
step 21: closing a fourth circuit breaker, and connecting the VSC into an output transformer of the wind power plant;
step 22: closing the second circuit breaker and the third circuit breaker in sequence;
step 23: when the output voltage of the stator winding tracks the voltage U of the upper connection pointsWhen so, the first circuit breaker is closed.
Preferably, after the LCC converter is controlled to operate in an inversion state in step 3, the LCC converter and the VSC converter are operated in parallel:
step 31: disconnecting the circuit breakers at the two ends of the submarine direct current cable;
step 32: switching the LCC converter to an inversion state;
step 33: collecting direct-current side voltage V of the VSC converterdc2Controlling the DC voltage V of the LCC converterdc1＝Vdc2Thereafter, the circuit breaker is closed.
Compared with the closest prior art, the excellent effects of the invention are as follows:
1. the method for starting the series-parallel direct-current power grid for large-scale long-distance offshore wind power integration can save a small alternating-current starting power supply (such as a diesel generator) for auxiliary starting at the wind power plant side, and save cost;
2. the control of the method for starting the parallel-serial direct-current power grid for large-scale long-distance offshore wind power integration is obtained by simplifying or blocking certain functions by a control method in steady-state operation, and a control program does not need to be independently written for the starting process.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1: the embodiment of the invention provides a flow chart of a starting method of a series-parallel direct-current power grid for large-scale long-distance offshore wind power integration;
FIG. 2: the structural schematic diagram of the parallel-serial direct current network of the large-scale long-distance offshore wind power grid connection in the embodiment of the invention;
FIG. 3: the schematic diagram of the topological structure of the VSC converter in the embodiment of the invention;
FIG. 4: the LCC converter in the embodiment of the invention has a topological structure schematic diagram;
FIG. 5: the embodiment of the invention is a locking charging schematic diagram;
FIG. 6: the embodiment of the invention provides a simplified grid-connected wiring diagram of a wind turbine generator.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The embodiment of the starting method of the series-parallel direct-current power grid for large-scale long-distance offshore wind power grid connection, provided by the invention, is shown in fig. 1, and the structure of the series-parallel direct-current power grid is shown in fig. 2 and comprises a VSC converter and an LCC converter; the VSC converter is connected to an offshore wind power plant, the LCC converter is connected to a land alternating current system, and the VSC converter and the LCC converter are connected through a submarine direct current cable. The method comprises the specific steps of carrying out,
and firstly, controlling the LCC converter to charge the VSC converter.
In this embodiment, the charging of the VSC converter by the LCC converter includes a lockout charging mode and a semi-lockout charging mode.
1. Latched charge mode, as shown in fig. 5:
(1) and controlling the LCC converter to work in a rectification state, and closing the circuit breakers at two ends of the submarine direct current cable.
(2) Voltage instruction V for controlling LCC converterdc1refStarting from 0, slowly increases linearly.
(3) And the direct current output by the LCC converter charges the capacitor through a diode of a submodule in the VSC converter.
In this embodiment, after the blocking charging mode is finished, the capacitor voltage of each sub-module is
Figure BDA0000894765270000041
Wherein, Vdc1NTo a rated value of DC voltage, NsmThe number of the sub-modules contained in each phase of bridge arm in the VSC converter is equal to the number of the sub-modules contained in each phase of bridge arm in the VSC converter.
2. Semi-latched charging mode:
(1) calculating the number n of sub-modules required to be input in the VSC converter,
Figure BDA0000894765270000042
wherein, VmIs the ac side line voltage peak.
(2) And carrying out capacitance voltage-sharing control on the VSC converter.
The capacitor voltage-sharing control strategy in this embodiment includes:
the method comprises the following steps: when the sub-modules are put into use, selecting the capacitor with the lowest voltage which is not put into the sub-modules, and putting the capacitor into use;
secondly, the step of: when the submodule is cut off, the highest capacitor voltage which is put into the submodule is selected and cut off;
③: and if the highest capacitor voltage in the sub-modules is higher than the lowest capacitor voltage in the sub-modules which are not put in by delta u, cutting off the highest capacitor voltage in the sub-modules which are put in, and putting in the lowest capacitor voltage in the sub-modules which are not put in. Δ u is the maximum deviation allowed between the highest of the sub-module capacitor voltages and the lowest of the sub-module capacitor voltages.
Fourthly, the method comprises the following steps: if the voltage of the switched-in sub-module is greater than VmaxThen, the voltage is cut off, and the input with the lowest capacitance voltage which is not input into the submodule is found out. VmaxIs the maximum value of the sub-module capacitor voltage.
Fifthly: and periodically detecting whether the number of the submodules needing to be put in is the same as the number of the put-in submodules, and if the number of the submodules is different, putting in or cutting off a certain number of the submodules to enable the number of the submodules to be consistent.
The capacitor voltage-sharing control is used for ensuring that the capacitor of the sub-module of the VSC converter is continuously charged; the capacitor voltage of all sub-modules is
Figure BDA0000894765270000051
When the charging process is finished, that is, in this embodiment, after the semi-locked charging mode is finished, the capacitor voltage of each sub-module is
Figure BDA0000894765270000052
Wherein, Vdc1NTo a rated value of DC voltage, NsmThe number of the sub-modules contained in each phase of bridge arm in the VSC converter is equal to the number of the sub-modules contained in each phase of bridge arm in the VSC converter.
And secondly, wind generating sets which are merged into the offshore wind farm one by one.
In the embodiment of the present invention, as shown in fig. 6:
a stator winding of the wind generating set is connected to an output transformer of the wind power plant through a first circuit breaker; the rotor winding is connected to the wind power plant output transformer through a third circuit breaker, a rotor side converter, a grid side converter and a second circuit breaker in sequence;
and the wind power plant output transformer is connected with the VSC converter through a fourth circuit breaker.
In the embodiment of the invention, the wind generating sets which are respectively merged into the offshore wind farm are not:
1. and closing the fourth circuit breaker, connecting the VSC into the wind power plant output transformer, and establishing reference voltage.
2. And closing the second circuit breaker and the third circuit breaker in sequence, and respectively establishing the direct current capacitor voltage and the stator winding output voltage of the wind turbine generator.
3. When the output voltage of the stator winding tracks the voltage U of the upper connection pointsAnd when the wind power generation system is in operation, the first breaker is closed, and smooth grid connection of the wind power generation set under the minimum impact current is realized.
And (4) grid-connecting the wind generating sets one by one according to the steps 1-3, wherein the active power output by the stator side of the wind generating set to the onshore alternating current system is 0.
And thirdly, controlling the LCC converter to work in an inversion state and then to run in parallel with the VSC converter.
In this embodiment, after the LCC converter operates in the inversion state, the specific steps of operating in parallel with the VSC converter are as follows:
1. and disconnecting the circuit breakers at the two ends of the submarine direct current cable.
2. And switching the LCC converter to an inversion state.
3. Collecting direct-current side voltage V of VSC converterdc2Controlling the DC voltage V of the LCC converterdc1＝Vdc2And then, closing the circuit breaker to complete the starting process of the parallel-serial direct current power grid, and transmitting the power generated by the offshore wind farm to the onshore alternating current power grid by using the parallel-serial direct current power grid.
Finally, it should be noted that: the described embodiments are only some embodiments of the present application and not all embodiments. 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 application.

Claims (2)

1. A starting method of a series-parallel direct-current power grid for large-scale long-distance offshore wind power grid connection is disclosed, wherein the series-parallel direct-current power grid comprises a VSC converter and an LCC converter; the VSC converter is connected to an offshore wind power plant, the LCC converter is connected to a land alternating current system, and the VSC converter and the LCC converter are connected through a submarine direct current cable, and the method is characterized by comprising the following steps:
step 1: controlling the LCC converter to charge the VSC converter;
step 2: wind generating sets are merged into the offshore wind farm one by one;
and step 3: controlling the LCC converter to work in an inversion state and then to run in parallel with the VSC converter;
a stator winding of the wind generating set in the step 2 is connected to a wind power plant output transformer through a first circuit breaker, and a rotor winding is connected to the wind power plant output transformer through a third circuit breaker, a rotor side converter, a grid side converter and a second circuit breaker in sequence; the wind power plant output transformer is connected with the VSC converter through a fourth circuit breaker;
and 2, wind generating sets which are merged into the offshore wind farm one by one:
step 21: closing a fourth circuit breaker, and connecting the VSC into an output transformer of the wind power plant;
step 22: closing the second circuit breaker and the third circuit breaker in sequence;
step 23: when the output voltage of the stator winding tracks the voltage U of the upper connection pointsWhen so, closing the first circuit breaker;
the step 1 that the LCC converter charges the VSC converter comprises a locking charging mode and a semi-locking charging mode;
the lockout charging mode:
step 111: controlling the LCC converter to work in a rectification state, and closing circuit breakers at two ends of the submarine direct current cable;
step 112: controlling a voltage command V of the LCC converterdc1refSlowly increasing linearly from 0;
step 113: the direct current output by the LCC converter charges a capacitor through a diode of a submodule in the VSC converter;
when the locking charging mode is finished, the capacitor voltage of each submodule is
Figure FDA0002594135400000021
Wherein, Vdc1NTo a rated value of DC voltage, NsmThe number of the sub-modules contained in each phase of bridge arm in the VSC converter is set;
the semi-latched charging mode:
step 121: calculating the number n of sub-modules required to be input in the VSC converter,
Figure FDA0002594135400000022
wherein VmIs the ac side line voltage peak;
step 122: carrying out capacitance voltage-sharing control on the VSC for ensuring the continuous charging of the capacitance of a sub-module of the VSC;
when the semi-locking charging mode is finished, the capacitor voltage of each submodule is
Figure FDA0002594135400000023
Wherein, Vdc1NTo a rated value of DC voltage, NsmThe number of the sub-modules contained in each phase of bridge arm in the VSC converter is equal to the number of the sub-modules contained in each phase of bridge arm in the VSC converter.
2. The method according to claim 1, wherein after the LCC converter is controlled to operate in the inverter state in step 3, the LCC converter is operated in parallel with the VSC converter:
step 31: disconnecting the circuit breakers at the two ends of the submarine direct current cable;
step 32: switching the LCC converter to an inversion state;
step 33: collecting direct-current side voltage V of the VSC converterdc2Controlling the DC voltage V of the LCC converterdc1＝Vdc2Thereafter, the circuit breaker is closed.
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CN110086198B (en) * 2019-04-23 2022-08-16 湖北工业大学 Multi-terminal hybrid direct-current power transmission system control method for offshore wind power grid connection
CN111541259B (en) * 2020-04-23 2021-07-30 南方电网科学研究院有限责任公司 Charging control method, device and medium for hybrid multi-terminal direct current transmission system
CN113612376B (en) * 2021-07-02 2023-02-28 广东电网有限责任公司阳江供电局 Starting method of offshore wind power direct current sending-out system

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