CN116154832A - SVG-based offshore wind power uncontrolled rectification direct current transmission system and control method - Google Patents
SVG-based offshore wind power uncontrolled rectification direct current transmission system and control method Download PDFInfo
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- CN116154832A CN116154832A CN202310430478.7A CN202310430478A CN116154832A CN 116154832 A CN116154832 A CN 116154832A CN 202310430478 A CN202310430478 A CN 202310430478A CN 116154832 A CN116154832 A CN 116154832A
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/1555—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit
- H02M7/1557—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit with automatic control of the output voltage or current
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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]
Abstract
The invention provides an offshore wind power uncontrolled rectification direct current transmission system based on SVG and a control method, belonging to the technical field of power electronics, wherein the system comprises: an offshore wind farm, an offshore converter station, a positive and negative pole seabed direct current sea cable, an onshore converter station and an onshore power grid; the alternating-current side of the offshore wind farm is connected with the alternating-current side of the offshore converter station through an offshore alternating-current bus; the direct current side of the offshore converter station is connected with the direct current side of the land converter station through a positive and negative electrode seabed direct current sea cable; the ac side of the land-based converter station is connected to the land-based grid. The invention can be compatible with the technical advantages of conventional direct current and flexible direct current, has low land making, small occupied area and small number of required submodules, can realize the light weight of an offshore platform, does not need a passive filter, and can be suitable for grid-connected power transmission occasions of offshore wind power plants under two different application situations of grid construction and grid following of offshore wind power.
Description
Technical Field
The application relates to the technical field of power electronics, in particular to an offshore wind power uncontrolled rectification direct current transmission system based on SVG and a control method.
Background
At present, offshore wind power enters a large-scale and commercial development stage, and has the characteristics of centralized development from offshore to offshore, shallow water to deep water and small-scale demonstration to large scale. In order to obtain more offshore wind energy resources, future offshore wind power projects will gradually develop to deep open sea. Because of the cable charging effect, the only feasible engineering scheme for long-distance cable transmission of the deep sea wind power is a direct current transmission scheme, however, the current direct current scheme generally adopts a scheme based on a flexible direct current transmission technology, power devices are numerous, a dry capacitor has large capacity value and heavy volume, the manufacturing cost is high, the problems of pain point needs to be solved mainly include two problems, namely, how to realize the light-weight platform and how to realize the reduction of the engineering cost.
Conventional direct current based on thyristors has the advantages of low manufacturing cost, mature technology and the like, but does not have the island network control characteristic and cannot provide grid-connected voltage for new energy units; similarly, the direct current transmission scheme based on the diode uncontrolled rectifying unit is lower in manufacturing cost, but has the same problem as the conventional direct current, namely grid-connected voltage cannot be provided for island offshore wind power. In addition, conventional dc power transmission requires a large number of passive filters to compensate for the reactive power it consumes and the harmonics that are generated.
How to consider the advantages of low cost, flexible control of flexible direct current and the like of the conventional direct current and better realize the large-scale deep open sea offshore wind power grid-connected digestion is the key of future technical development.
Disclosure of Invention
The invention aims to provide an offshore wind power uncontrolled rectification direct current transmission system based on SVG and a control method, and the method can be compatible with the technical advantages of conventional direct current and flexible direct current, has low land making, small occupied area and small number of required submodules, can realize the light weight of an offshore platform, does not need a passive filter, and can be suitable for offshore wind power plant grid-connected power transmission occasions under two different application situations of offshore wind power construction and grid following.
SVG-based offshore wind power uncontrolled rectification direct current transmission system comprises:
offshore wind farms, offshore converter stations, onshore converter stations and onshore grids;
an offshore converter station comprising:
the SVG unit and the six-pulse diode uncontrolled rectifying unit;
the SVG unit is arranged in parallel between the six-pulse diode uncontrolled rectifying unit and the converter transformer;
each six-pulse diode uncontrolled rectifying unit is provided with a set of SVG units, and the SVG units and the six-pulse diode uncontrolled rectifying units form a whole;
the SVG unit is responsible for voltage frequency support and active filtering, and the six-pulse diode uncontrolled rectifying unit is responsible for active power transmission;
the land-based converter station comprises:
an SVG unit and a thyristor rectification unit;
the thyristor rectifying unit is a twelve-pulse rectifying unit formed by two six-pulse thyristor rectifying units;
the SVG unit is arranged in parallel between the six-pulse thyristor rectifying unit and the converter transformer;
each six-pulse thyristor rectifying unit is provided with a set of SVG units, and the SVG units and the six-pulse thyristor rectifying units form a whole;
the SVG unit is responsible for reactive power compensation and active filtering, and the six-pulse thyristor rectifying unit is responsible for active power receiving and direct-current side voltage determining;
a grounding point is led out between the two six-pulse thyristor rectifying units, and the whole offshore wind power uncontrolled rectifying direct current system is only provided with the grounding point at the direct current side of the receiving end;
the alternating current side of the offshore wind farm is connected with the alternating current side of the offshore converter station;
the direct current side of the offshore converter station is connected with the direct current side of the land converter station;
the ac side of the land-based converter station is connected to the land-based grid.
Preferably, the diode uncontrolled rectifying unit is a twelve-pulse rectifying unit formed by two six-pulse diode rectifying units, and is used for transmitting active power output by the offshore wind farm to a direct current side, rectifying and transmitting the active power to an onshore converter station.
Preferably, the SVG unit is formed by star-shaped connection of three branches, and each branch is formed by cascading a plurality of full-bridge submodules and then is connected with a buffer reactor in series.
Preferably, a fast switch is configured at the neutral point of the first SVG unit and the second SVG unit;
a fast switch is arranged between the first six-pulse thyristor rectifying unit and the second six-pulse thyristor rectifying unit.
Preferably, the land-based converter station further comprises a start-up circuit arranged in the land-based converter station, in particular:
the land-based converter station starting loop is arranged at the network side of the land-based converter transformer;
the starting loop integrates a current measuring device, a starting resistor and a complete set of starting device with a single-blade isolating switch.
Amplitude and phase corrector are arranged on two sides of transformers of the offshore converter station and the onshore converter station, and the types and parameters of the amplitude and phase corrector are optimized according to system characteristics and resonance risks.
Preferably, the offshore wind power uncontrolled rectification direct current transmission system control method based on SVG comprises the following steps:
the land alternating current carries out uncontrolled charging on the land SVG unit through a starting resistor;
when the voltage reaches a limit value, the land alternating current controllably charges the land SVG unit until the land SVG unit is charged to a rated voltage value;
after the land SVG unit reaches the rated voltage, the land alternating current charges the offshore SVG unit controllably until the offshore SVG reaches the rated voltage value, and the starting of the offshore wind power uncontrolled rectifying direct current transmission system based on the SVG is completed.
Preferably, after the offshore wind power uncontrolled rectification direct current transmission system of the SVG is started, the method further comprises:
the six-pulse thyristor rectifying unit of the land convertor station adopts constant direct current voltage control, the SVG unit adopts constant reactive power control, and the SVG of the marine convertor station adopts constant alternating current voltage and alternating current frequency control;
gradually networking the offshore wind turbines of the offshore wind power plant.
Preferably, the offshore wind power uncontrolled rectification direct current transmission system control device based on SVG comprises:
the first land charging module is used for carrying out uncontrolled charging on the land SVG unit through the starting resistor by land alternating current;
the second land charging module is used for controllably charging the land SVG by the land alternating current until the land SVG unit is charged to a rated voltage value when the voltage reaches a limit value;
and the offshore charging module is used for controllably charging the offshore SVG by the onshore alternating current after the onshore SVG reaches the rated voltage until the offshore SVG unit reaches the rated voltage value.
Preferably, the computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor realizes the steps of any control method of the offshore wind power uncontrolled rectifying direct current transmission system based on SVG when executing the computer program.
Compared with the current mainstream flexible direct current transmission system, the invention reduces the number of submodules, the number of IGBTs and the number of capacitors, effectively reduces the volume and the weight, has the advantages of low cost, mature technology, portable platform and the like, and has great technical and economic competitiveness;
the invention adopts a diode uncontrolled rectifying unit at the transmitting end, and in the starting process, the onshore converter station realizes the black starting of the offshore wind farm by precharging the offshore station SVG; in normal operation, the offshore station SVG is matched with a diode valve to realize active power transmission and alternating voltage determination, wherein the SVG unit provides grid-connected voltage for an offshore wind farm;
the invention does not need to change the existing offshore wind farm control strategy, adopts mature technology, does not need to develop a large new technology, can rapidly realize engineering implementation, and has important popularization significance, so that the invention can be widely applied to the technical field of offshore wind power flexible direct current transmission.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a system block diagram of the present invention;
FIG. 2 is a flow chart of the method of the present invention;
FIG. 3 is a schematic diagram of a six-pulse diode rectifier unit according to the present invention;
FIG. 4 is a schematic diagram of a SVG unit based on a full-bridge submodule according to the present invention;
fig. 5 is a schematic diagram of a six-pulse thyristor unit of the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that all directional indicators (such as up, down, left, right, front, and rear … …) in the embodiments of the present invention are merely used to explain the relative positional relationship, movement, etc. between the components in a particular posture (as shown in the drawings), and if the particular posture is changed, the directional indicator is changed accordingly.
Furthermore, the description of "first," "second," etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention.
The long-distance direct current transmission scheme at the present stage generally adopts a scheme based on a flexible direct current transmission technology, a plurality of power devices are arranged, the capacity value of a dry capacitor is large, the size is heavy, the manufacturing cost is high, the conventional direct current based on a thyristor has the advantages of low manufacturing cost, mature technology and the like, the advantages of low cost, flexible control of the flexible direct current and the like of the conventional direct current are combined, the light platform is realized, and the engineering cost is reduced.
Example 1
SVG-based offshore wind power uncontrolled rectification direct current transmission system comprises:
offshore wind farms, offshore converter stations, onshore converter stations and onshore grids;
an offshore converter station comprising:
the SVG unit and the six-pulse diode uncontrolled rectifying unit;
the SVG unit is arranged in parallel between the six-pulse diode uncontrolled rectifying unit and the converter transformer;
each six-pulse diode uncontrolled rectifying unit is provided with a set of SVG units, and the SVG units and the six-pulse diode uncontrolled rectifying units form a whole;
the SVG unit is responsible for voltage frequency support and active filtering, and the six-pulse diode uncontrolled rectifying unit is responsible for active power transmission;
the land-based converter station comprises:
an SVG unit and a thyristor rectification unit;
the thyristor rectifying unit is a twelve-pulse rectifying unit formed by two six-pulse thyristor rectifying units;
the SVG unit is arranged in parallel between the six-pulse thyristor rectifying unit and the converter transformer;
each six-pulse thyristor rectifying unit is provided with a set of SVG units, and the SVG units and the six-pulse thyristor rectifying units form a whole;
the SVG unit is responsible for reactive power compensation and active filtering, and the six-pulse thyristor rectifying unit is responsible for active power receiving and direct-current side voltage determining;
a grounding point is led out between the two six-pulse thyristor rectifying units, and the whole offshore wind power uncontrolled rectifying direct current system is only provided with the grounding point at the direct current side of the receiving end;
the alternating current side of the offshore wind farm is connected with the alternating current side of the offshore converter station;
the direct current side of the offshore converter station is connected with the direct current side of the land converter station;
the ac side of the land-based converter station is connected to the land-based grid.
The system structure schematic diagram of the offshore wind power uncontrolled rectification direct current transmission system based on SVG is shown in fig. 1, and the reference numerals in the diagram are as follows:
1. an offshore wind farm; 11. a wind turbine generator; 12. an alternating current bus bar in the wind power plant; 13. a step-up transformer; the method comprises the steps of carrying out a first treatment on the surface of the 2. An offshore converter station; 21. marine ac bus (sink ac bus); 22. a first ac circuit breaker; 23. a second ac circuit breaker; 24. an offshore station amplitude and phase corrector; 25. a first transformer; 26. a second transformer; 27. a first SVG; 28. a second SVG; 29. a first six-pulse diode rectifying unit; 210. a second six-pulse diode rectifying unit; 211. a first DC switch; 212. a second DC switch; 3. a positive and negative pole submarine direct current submarine cable; 4. an onshore converter station; 41. a first six-ripple thyristor unit; 42. a second six-ripple thyristor unit; 43. a third SVG; 44. a fourth SVG; 45. a third transformer; 46. a fourth transformer; 47. an ac bus for land station; 48. a land standing amplitude phase corrector; 5. a land station ac start-up circuit; 51. starting a resistor to connect with a current measuring device in series; 52. starting a resistor bypass switch; 53. starting a resistor; 54. a wire inlet circuit breaker; 6. land grid.
Preferably, the diode uncontrolled rectifying unit is a twelve-pulse rectifying unit formed by two six-pulse diode rectifying units, and is used for transmitting active power output by the offshore wind farm to a direct current side, rectifying and transmitting the active power to an onshore converter station.
Preferably, the SVG unit is formed by star-shaped connection of three branches, and each branch is formed by cascading a plurality of full-bridge submodules and then is connected with a buffer reactor in series.
Preferably, a fast switch is configured at the neutral point of the first SVG unit and the second SVG unit;
a fast switch is arranged between the first six-pulse thyristor rectifying unit and the second six-pulse thyristor rectifying unit.
Preferably, the land-based converter station further comprises a start-up circuit arranged in the land-based converter station, in particular:
the land-based converter station starting loop is arranged at the network side of the land-based converter transformer;
the starting loop integrates a current measuring device, a starting resistor and a complete set of starting device with a single-blade isolating switch.
Preferably, the amplitude-phase corrector is arranged on both sides of the transformer of the offshore converter station and the transformer of the land converter station, and the type and parameters of the amplitude-phase corrector are optimized according to the characteristics of the system and the resonance risk.
As shown in fig. 1, the present embodiment provides an offshore wind power uncontrolled rectifying dc power transmission system based on SVG, which includes: an offshore wind farm 1, an offshore converter station 2, a positive and negative pole seabed direct current sea cable 3, a land converter station 4 (comprising an alternating current starting loop 5) and a land power grid 6 (a receiving end alternating current power grid). The alternating-current side of the offshore wind power plant 1 is connected with the alternating-current side of the offshore converter station 2 through an offshore alternating-current bus 21, and the direct-current side of the offshore converter station 2 is connected with the direct-current side of the onshore converter station 4 through a positive and negative ocean bottom direct-current sea cable 3; the ac side of the land-based converter station 4 is connected to a land-based grid 5.
As a preferred embodiment, the offshore wind farm 1 is formed by a plurality of wind turbines 12, which are collected on an ac bus to form a wind farm, and the wind farm is connected to the ac collection bus of the offshore converter station 2 by a step-up transformer.
As a preferred embodiment, as shown in fig. 1, the offshore converter station 2 mainly comprises 21, an offshore ac busbar (sink ac busbar); 22. a first ac circuit breaker; 23. a second ac circuit breaker; 24. an offshore station amplitude and phase corrector; 25. a first transformer; 26. a second transformer; 27. a first SVG unit; 28. a second SVG unit; 29. a first six-pulse diode rectifying unit; 210. a second six-pulse diode rectifying unit; 211. a first DC switch; 212. and a second DC switch. The device can be selectively configured according to system requirements, and the type and parameters of the amplitude-phase corrector are selected according to resonance risks and resonance degradation conditions.
As a preferred embodiment, the first transformer 25 is of YY coupling type, and the second transformer 26 is of YD coupling type. The first SVG unit 27 is arranged between the first transformer 25 and the first six-pulsating diode rectifying unit 29; the second SVG unit 28 is arranged between the second transformer 26 and the second six-pulsating diode rectifying unit 210. The device forms a twelve-pulse basic converter unit together, and the YY transformer and the YD transformer can mutually offset harmonic waves generated by a 6 n+/-1-time (wherein n is an odd number) diode rectifier unit. Therefore, the first SVG unit and the second SVG unit can filter out only 12 n+ -1 harmonics (where n is an integer), thereby reducing SVG branch harmonics. Since the SVG filters out harmonics at the transformer valve side, the SVG unit is configured at the network side to reduce many harmonics, thereby reducing harmonic loss, harmonic vibration, and the like. Because the characteristic harmonic wave generated by the diode rectifying unit is filtered by the SVG unit and counteracted by the transformer, only a very small amount of high-order non-characteristic harmonic wave can leak out, so that whether the amplitude-phase corrector is configured or not can be selected according to the specific system condition.
Preferably, the above-mentioned two converter units are included, and after any six-pulse converter unit fails, half of the power can be delivered.
As a preferred embodiment, the amplitude and phase corrector may select a double tuned structure or a high pass HP type structure.
Specifically, as shown in fig. 3, the six-pulse diode rectifying unit is formed by three-phase six bridge arms, each bridge arm is formed by a large number of high-power diodes, and the six-pulse diode rectifying unit has the characteristics of low manufacturing cost and light weight and is suitable for offshore station configuration.
Specifically, as shown in fig. 4, the SVG is formed by star-shaped connection of three branches, and each branch is cascaded by a plurality of full-bridge submodules and then serially connected with a buffer reactor L. The full bridge submodule is composed of four diode IGBTs (T11, D11), (T12, D12), (T21, D21) and (T21, D21).
As a preferred embodiment, a dc switch 211 is connected between the first SVG unit and the second SVG unit, and the low voltage end of the first six-pulse diode rectifying unit is connected to the high voltage end of the second six-pulse diode rectifying unit through a dc switch 212. The two dc switches are configured for the onshore converter station to precharge the offshore converter station SVG for black start. In normal operation, the first dc switch 211 is open and the second dc switch 212 is closed; during a black start process, the first dc switch 211 is closed and the second dc switch 212 is open. In particular, if the SVG precharge is started with an offshore station diesel engine, rather than a land station reverse charge, the dc switches 211, 212 may not be configured. At this time, no direct connection path exists between the first SVG unit and the second SVG unit, and the direct current side low voltage end of the first six-pulse diode rectifying unit is directly connected with the direct current side high voltage end of the second six-pulse diode rectifying unit.
As shown in fig. 1, the high-voltage end of the direct-current side of the first six-pulse diode rectifying unit is connected with an anode cable; and the direct-current side low-voltage end of the second six-pulse diode rectifying unit is connected with a negative cable.
As a preferred embodiment, the land based converter station 4 mainly comprises a six-ripple thyristor rectifying unit and a second filter 44, as shown in fig. 1, 3. The six-pulse thyristor rectifying unit is used for converting electric energy transmitted by the offshore wind farm 1 and sending the electric energy to the land power grid 5, and the second filter 44 is used for filtering high-frequency characteristic subharmonic noise.
As a preferred embodiment, the thyristor rectifying unit may be formed by a first six-pulse thyristor rectifying unit and a second six-pulse thyristor rectifying unit or directly adopts a twelve-pulse thyristor rectifying unit, and the specific form is required to correspond to the structure of the six-pulse diode uncontrolled rectifying unit in the offshore converter station.
When the land convertor station adopts two six-pulse thyristor rectifying units, the direct current sides of the first six-pulse thyristor rectifying unit and the second six-pulse thyristor rectifying unit are respectively connected with the anode and cathode submarine direct current sea cables through the direct current smoothing reactors in the station, and the alternating current sides of the first six-pulse thyristor rectifying unit and the second six-pulse thyristor rectifying unit are respectively connected with a land power grid through the amplitude-phase corrector and the starting loop 5.
Preferably, the smoothing reactor is a dry reactor.
Preferably, the land station amplitude corrector combines the risk of system oscillations and the degree of harmonic degradation to select whether to arrange. Depending on the system situation, the type and parameters of the amplitude and phase corrector are preferred.
Preferably, the starting circuit is composed of a starting resistor 53, a series current measuring device 51, and a starting resistor bypass switch 52. Wherein, for further saving of occupation of land, the starting circuit adopts integrated complete set starting device, and it integrates above-mentioned three group's parts, and wherein bypass switch can be the isolator of preferred area single sword. The starting resistor may preferably be a chip or ceramic resistor.
Example 2
A control method of an offshore wind power uncontrolled rectification direct current transmission system based on SVG comprises the following steps:
s100, performing uncontrolled charging on the land SVG by using land alternating current through a starting resistor;
s200, when the voltage reaches a limit value, the land alternating current charges the land SVG controllably until the land SVG is charged to a rated voltage value;
and S300, after the land SVG reaches the rated voltage, the land alternating current charges the offshore SVG controllably until the offshore SVG reaches the rated voltage value, and the starting of the offshore wind power uncontrolled rectification direct current transmission system based on the SVG is completed.
The invention discloses an offshore wind power uncontrolled rectifying direct current transmission system based on SVG, in the system, an offshore converter station (namely a transmitting end) adopts a modularized multi-level SVG unit and a diode uncontrolled rectifying unit, wherein the modularized multi-level SVG unit is configured between a converter transformer and the diode uncontrolled rectifying unit, the SVG is responsible for no-load control, a diode valve is responsible for active power transmission, a direct current side is connected with an onshore converter station (an inversion side) through a seabed direct current sea cable, and energy sent by an offshore wind power station is transmitted to an onshore alternating current station, and the onshore converter station simultaneously adopts the modularized multi-level SVG unit and the thyristor uncontrolled rectifying unit. The start-up process pre-charges the offshore station SVG submodule for start-up by the onshore station. During normal operation, the alternating-current side full-bridge MMC unit provides grid-connected voltage and frequency for the offshore wind farm, and the offshore wind farm wind driven generator can still be controlled by using the original conventional control strategy. The traditional direct current transmission technology of the SVG can achieve the technical effect similar to flexible direct current under the condition of keeping the equivalent investment scale of the conventional direct current, cancels an alternating current filter field, has the advantages of small occupied area, low manufacturing cost, low noise, great improvement of equipment reliability and safety and the like, can achieve large-scale island absorption of new energy, and has wide application prospects in the aspects of delivering new energy to a northwest Sha Gehuang base, delivering clean energy to a southwest base and offshore wind power.
After the S300SVG offshore wind power uncontrolled rectification direct current transmission system is started, the method further comprises the following steps:
the LCC thyristor rectifying unit of the land convertor station adopts constant direct current voltage control, SVG adopts constant reactive power control, and SVG of the marine convertor station adopts constant alternating current voltage and alternating current frequency control;
gradually networking the offshore wind turbines of the offshore wind power plant.
The embodiment provides a control method of an offshore wind power uncontrolled rectification direct current transmission system, which specifically comprises the following steps:
(1) A precharge start ready state, in which the off-shore station ac breakers 22, 23 are opened, the off-shore station SVG inter-cell switch 211 is closed, and the off-shore station six-pulse diode rectifying inter-cell switch 212 is opened; the land station ac breaker 54 and the firing resistor bypass switch 52 are opened.
(2) The onshore station ac breaker 54 is closed and the onshore ac current is used to precharge the onshore SVG submodule capacitors in an uncontrolled phase through the start-up resistor.
(3) When a certain limit of the capacitor voltage is reached, the start-up resistor bypass breaker 52 is closed and the controllable charging phase is entered until the SVG unit is charged to the rated voltage.
(4) The thyristor valve is unlocked and the firing angle is controlled such that the dc voltage is negative and the offshore station first and second SVG units are charged uncontrollably via the switch 211 through the dc side.
(5) And after the capacitor voltage reaches a certain limit value, unlocking the offshore station SVG to perform controllable charging, and achieving the rated value of the capacitor voltage of the submodule.
(6) Switch 211 is opened and switches 212, 22, 23 are closed. Offshore and onshore stations are brought into normal operation mode.
(7) In normal operation, the LCC thyristor rectifying unit of the land station adopts constant direct current voltage control, SVG adopts constant reactive power control, and the SVG of the marine station adopts constant alternating current voltage and alternating current frequency control. In addition, the offshore station and the onshore station SVG perform harmonic compensation control, and the filtering times such as 12 n+/-1 times can be optimized according to the system requirement, wherein 6 (2 n) +/-1 can be counteracted with the upper six-pulse unit transformer and the lower six-pulse unit transformer.
(8) After an alternating current network is established, gradually networking the offshore wind turbines.
Example 3
SVG-based offshore wind power uncontrolled rectification direct current transmission system control device comprises:
the first land charging module is used for carrying out uncontrolled charging on the land SVG by the land alternating current through the starting resistor;
the second land charging module is used for controllably charging the land SVG until the land SVG is charged to a rated voltage value when the voltage reaches a limit value;
and the offshore charging module is used for controllably charging the offshore SVG after the offshore SVG reaches the rated voltage until the offshore SVG reaches the rated voltage value.
Example 4
A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor realizes the steps of any control method of the offshore wind power uncontrolled rectifying direct current transmission system based on SVG when executing the computer program.
Compared with the current mainstream flexible direct current transmission system, the invention reduces the number of submodules, the number of IGBTs and the number of capacitors, effectively reduces the volume and the weight, has the advantages of low cost, mature technology, portable platform and the like, and has great technical and economic competitiveness;
the invention adopts a diode uncontrolled rectifying unit at the transmitting end, and in the starting process, the onshore converter station realizes the black starting of the offshore wind farm by precharging the offshore station SVG; in normal operation, the offshore station SVG is matched with a diode valve to realize active power transmission and alternating voltage determination, wherein the SVG unit provides grid-connected voltage for an offshore wind farm;
the invention does not need to change the existing offshore wind farm control strategy, adopts mature technology, does not need to develop a large new technology, can rapidly realize engineering implementation, and has important popularization significance, so that the invention can be widely applied to the technical field of offshore wind power flexible direct current transmission.
The foregoing is only a specific embodiment of the invention to enable those skilled in the art to understand or practice the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. SVG-based offshore wind power uncontrolled rectification direct current transmission system is characterized by comprising:
offshore wind farms, offshore converter stations, onshore converter stations and onshore grids;
the offshore converter station comprises:
the SVG unit and the six-pulse diode uncontrolled rectifying unit;
the SVG unit is arranged in parallel between the six-pulse diode uncontrolled rectifying unit and the converter transformer;
each six-pulse diode uncontrolled rectifying unit is provided with a set of SVG units, and the SVG units and the six-pulse diode uncontrolled rectifying units form a whole;
the SVG unit is responsible for voltage frequency support and active filtering, and the six-pulse diode uncontrolled rectifying unit is responsible for active power transmission;
the land-based converter station includes:
an SVG unit and a thyristor rectification unit;
the thyristor rectifying unit is a twelve-pulse rectifying unit formed by two six-pulse thyristor rectifying units;
the SVG unit is arranged in parallel between the six-pulse thyristor rectifying unit and the converter transformer;
each six-pulse thyristor rectifying unit is provided with a set of SVG units, and the SVG units and the six-pulse thyristor rectifying units form a whole;
the SVG unit is responsible for reactive power compensation and active filtering, and the six-pulse thyristor rectifying unit is responsible for active power receiving and direct-current side voltage determination;
the grounding point is led out between the two six-pulse thyristor rectifying units, and the whole offshore wind power uncontrolled rectifying direct current system is only provided with the grounding point at the direct current side of the receiving end;
the alternating current side of the offshore wind farm is connected with the alternating current side of the offshore converter station;
the direct current side of the offshore converter station is connected with the direct current side of the land converter station;
the ac side of the land-based converter station is connected to the land-based grid.
2. The offshore wind power uncontrolled rectifying direct current transmission system based on SVG according to claim 1, wherein the diode uncontrolled rectifying unit is a twelve-pulse rectifying unit formed by two six-pulse diode rectifying units, and is used for transmitting active power output by an offshore wind farm to a direct current side for rectifying and then transmitting to an onshore converter station.
3. The offshore wind power uncontrolled rectifying direct current transmission system based on SVG according to claim 1, wherein the SVG unit is formed by star connection of three branches, and each branch is connected in series with a buffer reactor after being cascaded by a plurality of full-bridge submodules.
4. The SVG-based offshore wind power uncontrolled rectified dc transmission system of claim 1, wherein a fast switch is configured at the neutral point of the first SVG unit and the second SVG unit;
a fast switch is arranged between the first six-pulse thyristor rectifying unit and the second six-pulse thyristor rectifying unit.
5. The SVG-based offshore wind power uncontrolled rectified direct current transmission system of claim 1, wherein the onshore converter station further comprises a start loop arranged at the onshore converter station, in particular:
the land-based converter station starting loop is arranged at the network side of the land-based converter transformer;
the starting loop integrates a current measuring device, a starting resistor and a complete set of starting device with a single-blade isolating switch.
6. The SVG-based offshore wind power uncontrolled rectified direct current transmission system according to claim 1, wherein the amplitude-phase corrector is configured on both sides of the offshore converter station and the land converter station transformer, and the type and parameters of the amplitude-phase corrector are optimized according to the system characteristics and resonance risks.
7. The control method of the offshore wind power uncontrolled rectification direct current transmission system based on SVG is characterized by comprising the following steps:
the land alternating current carries out uncontrolled charging on the land SVG unit through a starting resistor;
when the voltage reaches a limit value, the land alternating current controllably charges the land SVG unit until the land SVG unit is charged to a rated voltage value;
after the land SVG unit reaches the rated voltage, the land alternating current charges the offshore SVG unit controllably until the offshore SVG reaches the rated voltage value, and the starting of the offshore wind power uncontrolled rectifying direct current transmission system based on the SVG is completed.
8. The method for controlling an offshore wind power uncontrolled rectifying dc power transmission system based on SVG according to claim 7, wherein after the offshore wind power uncontrolled rectifying dc power transmission system of SVG is started, the method further comprises:
the six-pulse thyristor rectifying unit of the land convertor station adopts constant direct current voltage control, the SVG unit adopts constant reactive power control, and the SVG unit of the marine convertor station adopts constant alternating current voltage and alternating current frequency control;
gradually networking the offshore wind turbines of the offshore wind power plant.
9. SVG-based offshore wind power uncontrolled rectification direct current transmission system control device is characterized by comprising:
the first land charging module is used for carrying out uncontrolled charging on the land SVG unit through the starting resistor by land alternating current;
the second land charging module is used for controllably charging the land SVG by the land alternating current until the land SVG unit is charged to a rated voltage value when the voltage reaches a limit value;
and the offshore charging module is used for controllably charging the offshore SVG by the onshore alternating current after the onshore SVG reaches the rated voltage until the offshore SVG unit reaches the rated voltage value.
10. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the SVG-based offshore wind power uncontrolled rectified direct current transmission system control method of any one of claims 7 to 8.
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