CN116646953A - Multi-stage traversing control method and device for alternating current asymmetric faults of offshore wind farm - Google Patents

Multi-stage traversing control method and device for alternating current asymmetric faults of offshore wind farm Download PDF

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Publication number
CN116646953A
CN116646953A CN202310585919.0A CN202310585919A CN116646953A CN 116646953 A CN116646953 A CN 116646953A CN 202310585919 A CN202310585919 A CN 202310585919A CN 116646953 A CN116646953 A CN 116646953A
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Prior art keywords
offshore
energy
wind farm
offshore wind
fault
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Inventor
姚伟
赵海宇
周泓宇
艾小猛
文劲宇
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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Priority to CN202310585919.0A priority Critical patent/CN116646953A/en
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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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • 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
    • 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
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a multi-stage ride-through control method and device for alternating-current asymmetric faults of an offshore wind farm, belonging to the field of control of power systems, wherein the method comprises the following steps: when an alternating current asymmetric fault is detected, reactive compensation and current amplitude limiting control are carried out on the offshore wind farm; starting sequence net energy control of the offshore converter station, so as to inhibit negative sequence current components under alternating current asymmetric faults through positive and negative sequence decomposition control, and calculating energy absorption slope through active energy control; controlling an offshore converter station to absorb energy output by an offshore wind farm at a rate corresponding to an energy absorption slope; when the AC asymmetry fault is detected to be cleared, calculating an energy release slope, and controlling the offshore converter station to release energy to an onshore AC power grid at a rate corresponding to the energy release slope. The alternating current asymmetric fault ride-through capability of the offshore wind farm and the flexible direct current converter station is improved, and the efficient consumption of renewable energy sources and the economical efficiency of the offshore wind farm grid-connected system can be promoted.

Description

Multi-stage traversing control method and device for alternating current asymmetric faults of offshore wind farm
Technical Field
The invention belongs to the field of power system control, and particularly relates to a multi-stage traversing control method and device for alternating current asymmetric faults of an offshore wind farm.
Background
Offshore wind farms are an important means of supporting large-scale renewable energy grid-connected operation. Conventional offshore wind power engineering typically incorporates an ac subsea cable into an onshore ac grid. The grid connection mode of high-voltage direct current transmission (Modular Multilevel Converter based High Voltage Direct Current, MMC-HVDC) through the modularized multi-level converter has obvious advantages, after being collected, each offshore wind turbine unit is converted into high-voltage direct current at an offshore converter station, electric energy is sent out through a submarine cable, and then is converted into alternating current at an onshore converter station and finally is injected into an onshore alternating current system.
An ac asymmetric fault is a fault with high probability of occurrence at sea and high proportion of faults, and the fault position is between an offshore wind farm and a farm side converter station (WFMMC). The offshore wind farm lacks support of an onshore power grid, and the fault characteristic presents a complex double-sided power electronic power supply characteristic; in addition, due to the low overcurrent and low overvoltage characteristics of the power electronic devices, the problem of multi-stage voltage and current fault ride-through of the WFMMC and the offshore wind farm under the offshore alternating current fault is more remarkable. Therefore, how to solve the problem of the offshore alternating current asymmetric fault ride-through is important to the grid connection stability of the offshore wind farm.
Around the above problems, the existing engineering solutions are often only equipped with a negative sequence current elimination control strategy, or negative sequence current control is added to both the offshore wind farm and the WFMMC, so that the offshore alternating current asymmetric fault ride-through requirements cannot be completely met. The low-voltage current limiting control strategy is adopted by the WFMMC side by a learner to solve the problem of overcurrent of power electronic devices under faults, but the active drop of voltage can cause the fan to be off-grid due to low voltage in consideration of the low-voltage ride through requirement of a wind power plant. In view of the above, research on the offshore ac asymmetric short-circuit fault is still imperfect, and further excavating the fault mechanism is needed, and an effective fault crossing scheme is proposed on the basis of the further excavating the fault mechanism.
Disclosure of Invention
Aiming at the defects and improvement demands of the prior art, the invention provides a multi-stage traversing control method and device for alternating current asymmetric faults of an offshore wind farm, and aims to enable offshore wind power to realize fault traversing control of the alternating current asymmetric short circuit faults through a soft direct grid-connected system and realize multi-stage fault traversing so as to improve alternating current asymmetric fault traversing capacity of the system.
To achieve the above object, according to one aspect of the present invention, there is provided a multi-stage ride-through control method of an ac asymmetric fault of an offshore wind farm for a system comprising the offshore wind farm, an offshore converter station and an onshore ac grid, the method comprising: when an alternating current asymmetric fault is detected to occur on the offshore side of the system, reactive compensation and current amplitude limiting control are carried out on the offshore wind farm; starting sequence network energy control of the offshore converter station to inhibit a negative sequence current component under an alternating current asymmetric fault through positive and negative sequence decomposition control, and calculating an energy absorption slope of the first-stage sequence network energy control through active energy control; and controlling the offshore converter station to absorb the energy output by the offshore wind farm at a rate corresponding to the energy absorption slope; when the AC asymmetric fault is detected to be cleared, calculating the energy release slope of the energy control of the second-stage sequence network through the active energy control, and controlling the offshore converter station to release energy to the onshore AC power network at the rate corresponding to the energy release slope.
Still further, when the ac asymmetry fault is detected to be cleared, the method further comprises: and calculating an outer ring voltage reference value through additional alternating voltage outer ring inhibition, and controlling the offshore converter station according to the outer ring voltage reference value so as to avoid overvoltage of an offshore grid-connected point.
Still further, the outer loop voltage reference value is:
U sdref2 ＝U sdref +K p (U sdref- U sdpu )
wherein ,Usdref 、U sdref2 Respectively the external ring voltage reference values before and after the external ring suppression of the additional alternating voltage, U sdpu Is the per unit value, K of the amplitude of the AC voltage at the grid-connected point p Is a compensation coefficient.
Further, reactive power compensation reference value Q of the offshore wind farm when reactive power compensation is performed ref The method comprises the following steps:
i sqref ≥1.5×(0.9-U sd )I s
wherein ,Usd D-axis component of offshore grid-tie voltage for incorporation of offshore wind farms into offshore converter stations, I s Output current amplitude, i, for offshore wind farm sdref 、i sqref Reference values i of current inner ring d and q axis currents of offshore wind power plant respectively smax The maximum amplitude of the current output by the ring of the offshore wind farm is set; according to i smax And performing current limiting control.
Still further, the energy absorption slope is:
wherein ,k1 For the energy absorption slope, P s For real-time power value, P, output by offshore wind farm acmax Maximum value of alternating current power output to offshore converter station for offshore wind farm, P dc Real-time DC power, deltaW, for an offshore wind farm to be output to an offshore converter station WFMMC For varying the energy value of the offshore converter station, U sj1 、U sj2 J-phase sampling values of the offshore grid-connected voltage before and after a fault sampling period respectively, wherein DeltaT is a faultSampling period, W WFMMCmax For the maximum upper limit of the energy of the offshore converter station, U sjmax Maximum values are allowed for j phase shunt voltage operation, j=a, b, c.
Further, the energy change relation of the offshore converter station in the energy control process of the first phase sequence network is as follows:
wherein ,is equivalent electromotive force of WFMMC side, +.>For the grid-connected equivalent voltage after the energy control of the first stage sequence network is put into the submodule, Z MMC Equivalent reactance of MMC side, +.>For MMC side alternating current, +.>For the fault voltage formed at the fault point, W MMC For real-time value of converter station energy, C arm As an average value of the capacitance of the sub-module,sub-module voltage average values P of upper bridge arm and lower bridge arm of j phases respectively ac Real-time ac power output to an offshore converter station for an offshore wind farm, U dc 、I dc The DC voltage value and the DC current value of the offshore DC submarine cable are respectively set.
Still further, the energy release slope is:
wherein ,k2 For the energy release slope, S N For rated reference capacity of system, W WFMMC0 For steady state energy value, P, of an offshore converter station under nominal operating conditions dc 、P ac The real-time direct current power and the real-time alternating current power which are respectively output to the offshore converter station by the offshore wind farm.
Still further, before the step of starting the sequence grid energy control of the offshore converter station, the method further comprises: the three-phase circuit parameters are converted into circuit parameters in a sequence network for calculating the energy absorption slope and the energy release slope.
According to another aspect of the present invention there is provided a multi-stage ride-through control device for an ac asymmetric fault of an offshore wind farm for a system comprising the offshore wind farm, an offshore converter station and an onshore ac grid, the device comprising: the compensation and amplitude limiting module is used for carrying out reactive compensation and current amplitude limiting control on the offshore wind farm when an alternating current asymmetric fault on the offshore side of the system is detected; the first phase sequence network energy control module is used for starting sequence network energy control of the offshore converter station so as to inhibit a negative sequence current component under an alternating current asymmetric fault through positive and negative sequence decomposition control, and calculating an energy absorption slope of the first phase sequence network energy control through active energy control; and controlling the offshore converter station to absorb the energy output by the offshore wind farm at a rate corresponding to the energy absorption slope; and the second-stage sequence network energy control module is used for calculating the energy release slope of the second-stage sequence network energy control through the active energy control when the AC asymmetric fault is detected to be cleared, and controlling the offshore converter station to release energy to the onshore AC power grid at the rate corresponding to the energy release slope.
According to another aspect of the present invention there is provided a computer readable storage medium having stored thereon a computer program, characterized in that the program when executed by a processor implements a multi-stage ride-through control method of an offshore wind farm ac asymmetry fault as described above.
In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:
(1) The multi-stage traversing control method for the alternating current asymmetric faults of the offshore wind farm is provided, and two-stage sequence network energy control is performed based on the fault traversing requirements of three stages of fault period, fault steady state and fault recovery existing in the offshore alternating current asymmetric faults; during the fault period and the fault steady-state period, the fault phase current amplitude is reduced by the fault phase input submodule to realize self-adaptive energy control, so that the current impact on the offshore converter station is reduced; after the fault is recovered, the energy is released back to the onshore alternating current power grid, so that the alternating current asymmetric fault ride-through capability of the offshore wind farm and the offshore converter station is improved, the efficient consumption of renewable energy sources can be promoted, and the economical efficiency of the offshore wind farm grid-connected system is improved;
(2) After the fault is recovered, the overvoltage of the grid-connected point after the fault is recovered is avoided by adding the outer ring inhibition of the alternating voltage so as to meet the requirement of high voltage ride through.
Drawings
FIG. 1 is a flow chart of a multi-stage ride-through control method for alternating-current asymmetric faults of an offshore wind farm provided by an embodiment of the invention;
FIG. 2 is a control block diagram of a multi-stage ride-through control method for alternating-current asymmetric faults of an offshore wind farm provided by an embodiment of the invention;
fig. 3A, fig. 3B, fig. 3C, fig. 3D, fig. 3E, fig. 3F, fig. 3G, and fig. 3H are schematic diagrams of grid-connected voltage of an offshore wind farm, fault current of a WFMMC, fault current of a grid-side converter (Grid Side Converter, GSC), fault current comparison, energy variation of the WFMMC, WFMMC valve-side voltage, grid-connected voltage of a land ac system, and negative sequence component of the fault current under control of a corresponding method in a single-phase grounding scenario provided by an embodiment of the present invention;
fig. 4A, fig. 4B, fig. 4C, fig. 4D, fig. 4E, and fig. 4F are schematic diagrams of grid-connected voltage, B-phase fault current, C-phase fault current, energy variation of WFMMC, each sequence component of grid-connected voltage, and negative sequence component of fault current of the offshore wind farm under control of the corresponding method in the two-phase grounding scenario provided by the embodiment of the present invention;
fig. 5A, fig. 5B, fig. 5C, fig. 5D, fig. 5E, and fig. 5F are schematic diagrams of two-phase inter-phase fault voltage, B-phase fault current, C-phase fault current, energy variation of WFMMC, each sequence component of grid-connected voltage, and negative sequence component of fault current under control of the corresponding method provided by the embodiment of the invention;
FIG. 6 is a block diagram of a multi-stage ride-through control device for an AC asymmetric fault in an offshore wind farm provided by an embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
In the present invention, the terms "first," "second," and the like in the description and in the drawings, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.
Fig. 1 is a flowchart of a multi-stage ride-through control method for alternating-current asymmetric faults of an offshore wind farm according to an embodiment of the present invention. Referring to fig. 1, in conjunction with fig. 2 to 5F, a multi-stage traversing control method for ac asymmetric faults of an offshore wind farm in this embodiment is described in detail, and the method includes operations S1 to S3.
And (S1) when the AC asymmetric fault on the offshore side of the system is detected, reactive compensation and current limiting control are carried out on the offshore wind farm.
The method is used in a system comprising an offshore wind farm, an offshore converter station and an onshore ac grid, as shown in fig. 2, the system further comprising an onshore converter station. The electric energy generated by the offshore wind farm is converted into high-voltage direct current at the offshore converter station, then is transmitted to the onshore converter station through the direct current sea cable, is converted into alternating current by the onshore converter station, and is injected into an onshore alternating current power grid. The method in the embodiment is to control the offshore wind farm and the offshore converter station when an ac asymmetric fault occurs on the offshore side.
In this embodiment, the fault detection process is as follows: when the drop value of the grid-connected voltage of the offshore wind farm exceeds the voltage drop threshold value of the fault detection unit, judging whether the fault type is an alternating current asymmetric fault or not according to the drop value.
Further, determining fault depth and voltage drop degree according to the drop value, and according to the obtained fault depth and voltage drop degree, enabling the offshore converter station to be equivalent to a controlled voltage source or a controlled current source, and enabling the offshore wind farm to be equivalent to the controlled current source.
When an alternating current asymmetric fault is detected, reactive compensation and current amplitude limiting control of the offshore wind power plant and multi-stage sequence network energy control of the offshore converter station are respectively started through certain communication delay.
According to an embodiment of the invention, the reactive power compensation reference value Q of the offshore wind farm for the fault location ref The method comprises the following steps:
i sqref ≥1.5×(0.9-U sd )I s
wherein ,Usd D-axis component of offshore grid-tie voltage for incorporation of offshore wind farms into offshore converter stations, I s Output current amplitude, i, for offshore wind farm sdref 、i sqref Reference values i of current inner ring d and q axis currents of offshore wind power plant respectively smax The maximum amplitude of the current output by the ring of the offshore wind farm is set; according to i smax And performing current limiting control. i.e smax For example takingThe value was 1.2.
Operation S2, starting sequence network energy control of the offshore converter station to inhibit a negative sequence current component under an alternating current asymmetric fault through positive and negative sequence decomposition control, and calculating an energy absorption slope of the first-stage sequence network energy control through active energy control; and controlling the offshore converter station to absorb the energy output by the offshore wind farm at a rate corresponding to the energy absorption slope.
In this embodiment, the sequence net energy control includes positive and negative sequence decomposition control and active energy control. After an alternating current asymmetric fault occurs, setting a reference value of negative sequence current as 0, calculating an absorption slope of self-adaptive energy control of the offshore converter station and an outer loop reactive power reference value of the offshore wind power plant, and realizing self-adaptive energy control by throwing sub-modules into a fault phase to reduce the amplitude of the fault phase current, reduce current impact on the offshore converter station, and realize series voltage division by throwing additional sub-modules into a non-fault phase to actively prevent the non-fault phase from being over-voltage.
In the first stage, negative sequence current components under alternating current asymmetric faults are restrained through positive and negative sequence decomposition control, and energy output by the offshore wind farm is absorbed through active energy control.
According to an embodiment of the invention, before starting the sequence net energy control of the offshore converter station, the method further comprises: the three-phase circuit parameters are converted to circuit parameters in a sequence net for calculating an energy absorption slope and an energy release slope. The transformation process is as follows:
wherein ,for three-phase circuit parameters>The method is characterized in that the method is a circuit parameter in a sequence network, and A is a transformation matrix; α=1 < 120° for rotating the unit vector counterclockwise by 120 °.
Starting the active energy control of the WFMMC (i.e. the offshore converter station), the energy absorption slope is calculated in the following way:
the specific expression mode of the formula is as follows:
wherein ,k1 P for energy absorption slope s For real-time power value, P, output by offshore wind farm acmax Maximum value of alternating current power output to offshore converter station for offshore wind farm, P dc Real-time DC power, deltaW, for an offshore wind farm to be output to an offshore converter station WFMMC For varying the energy value of the offshore converter station, U sj1 、U sj2 J-phase sampling values of the offshore grid-connected voltage before and after a fault sampling period respectively, wherein DeltaT is a fault sampling period and W is a fault sampling period WFMMCmax For the maximum upper limit of the energy of the offshore converter station, U sjmax Maximum values are allowed for j phase shunt voltage operation, j=a, b, c. k (k) 0 And (5) the energy absorption slope of the offshore converter station is the energy absorption slope of the offshore wind farm grid-connected phase overvoltage phenomenon.
The energy change relation of the offshore converter station in the energy control process of the first phase sequence network is as follows:
wherein ,is equivalent electromotive force of WFMMC side, +.>For the grid-connected equivalent voltage after the energy control of the first stage sequence network is put into the submodule, Z MMC Equivalent reactance of MMC side, +.>For MMC side alternating current, +.>For the fault voltage formed at the fault point, W MMC For real-time value of converter station energy, C arm As an average value of the capacitance of the sub-module,sub-module voltage average values P of upper bridge arm and lower bridge arm of j phases respectively ac Real-time ac power output to an offshore converter station for an offshore wind farm, U dc 、I dc The DC voltage value and the DC current value of the offshore DC submarine cable are respectively set.
And S3, when the AC asymmetric fault is detected to be cleared, calculating the energy release slope of the energy control of the second-stage sequence network through the active energy control, and controlling the offshore converter station to release energy to an onshore AC power grid at a rate corresponding to the energy release slope.
In the second stage, positive and negative sequence decomposition control is always in a starting state, and after the alternating current asymmetric fault is cleared, no negative sequence current component exists, so that the negative sequence current component does not need to be restrained; the energy is released by active energy control.
According to an embodiment of the invention, the energy release slope is:
wherein ,k2 For the slope of energy release S N For rated reference capacity of system, W WFMMC0 For steady state energy value, P, of an offshore converter station under nominal operating conditions dc 、P ac The real-time direct current power and the real-time alternating current power which are respectively output to the offshore converter station by the offshore wind farm.
The energy change relation of the offshore converter station in the second-stage sequence network energy control process is as follows:
wherein at this timeAnd the grid-connected equivalent voltage is controlled by the energy of the second-stage grid sequence after being input into the sub-module.
According to an embodiment of the invention, when it is detected that the ac asymmetry fault is cleared, the method further comprises: and calculating an outer ring voltage reference value by adding an outer ring suppression of alternating voltage, and controlling the offshore converter station according to the outer ring voltage reference value so as to avoid overvoltage of an offshore grid-connected point, thereby meeting the requirement of high voltage ride through. The outer loop voltage reference value is:
U sdref2 ＝U sdref +K p (U sdref- U sdpu )
wherein ,Usdref 、U sdref2 Respectively the external ring voltage reference values before and after the external ring suppression of the additional alternating voltage, U sdpu Is the per unit value, K of the amplitude of the AC voltage at the grid-connected point p Is a compensation coefficient.
In the embodiment, through the active energy release and voltage compensation control of the offshore converter station, the phenomenon of overvoltage recovery is avoided in the fault recovery stage, the offshore stored energy can be released into the offshore alternating current power grid again, the effective utilization of the energy is realized, and the consumption of offshore wind power and wind energy is promoted.
In order to verify the practicability of the embodiment of the invention, the embodiment carries out simulation experiments under different offshore alternating current asymmetric short-circuit faults. The corresponding simulation results under the conditions of the method of the embodiment of the invention and the existing negative sequence current suppression method under the marine alternating current asymmetric single-phase grounding short-circuit fault are shown in fig. 3A, 3B, 3C, 3D, 3E, 3F, 3G and 3H. The corresponding simulation results under the current suppression method of the embodiment of the invention and the existing negative sequence current under the condition of the offshore alternating current asymmetric two-phase grounding short circuit fault are shown in fig. 4A, 4B, 4C, 4D, 4E and 4F. The simulation results of the two-phase-to-phase correspondence under the current suppression method of the embodiment of the invention and the existing negative sequence current under the marine alternating current asymmetric two-phase grounding short circuit fault are shown in fig. 5A, 5B, 5C, 5D, 5E and 5F. Referring to fig. 3A to fig. 5F, it can be known that, compared with the existing negative sequence current suppression method, the multi-stage traversing control method in this embodiment can realize the fault traversing of the offshore ac asymmetric fault, promote the efficient absorption of renewable energy sources and improve the economy of the offshore wind farm grid-connected system.
According to the multistage crossing control method for the alternating current asymmetric faults of the offshore wind farm, disclosed by the embodiment of the invention, the multistage crossing control is performed based on the multi-stage fault crossing requirements of the alternating current asymmetric faults at sea, and the multistage crossing control method specifically comprises three stages of fault crossing during fault period, fault steady state and fault recovery. During the fault period and the fault steady-state period, the self-adaptive energy control is realized by reducing the current amplitude of the fault phase in the fault phase throwing submodule, the current impact on the offshore converter station is reduced, the additional submodule realizes series voltage division in the non-fault phase throwing, and the non-fault phase fault overvoltage is actively prevented; after the fault is recovered, the overvoltage of the grid-connected point after the fault is recovered is avoided by adding the outer ring inhibition of the alternating voltage, and the requirement of high voltage ride through is met. Therefore, the alternating current asymmetric fault ride-through can be realized in the aspects of power supply equivalence, negative sequence inhibition, energy control and voltage stabilization, the alternating current asymmetric fault ride-through capability of the offshore wind farm and the offshore converter station is improved, and the efficient consumption of renewable energy sources and the economical efficiency of the offshore wind farm grid-connected system can be promoted.
FIG. 6 is a block diagram of a multi-stage ride-through control device for an AC asymmetric fault in an offshore wind farm provided by an embodiment of the invention. Referring to fig. 6, the multi-stage ride-through control device 600 for ac asymmetric faults of an offshore wind farm includes a compensation and limiting module 610, a first stage sequence grid energy control module 620, and a second stage sequence grid energy control module 630.
The compensation and clipping module 610 performs, for example, operation S1 for reactive compensation and current clipping control of the offshore wind farm upon detection of an ac asymmetry fault on the offshore side of the system.
The first phase sequence grid energy control module 620, for example, performs operation S2 for initiating sequence grid energy control of the offshore converter station to suppress the negative sequence current component under the ac asymmetric fault by positive-negative sequence decomposition control, and calculates the energy absorption slope of the first phase sequence grid energy control by active energy control; and controlling the offshore converter station to absorb the energy output by the offshore wind farm at a rate corresponding to the energy absorption slope.
The second phase sequence grid energy control module 630 performs, for example, operation S3, for calculating an energy release slope of the second phase sequence grid energy control by active energy control when the ac asymmetry fault is detected to be cleared, and controlling the offshore converter station to release energy to the onshore ac grid at a rate corresponding to the energy release slope.
The multi-stage ride-through control device 600 for offshore wind farm ac asymmetric faults is used to perform the multi-stage ride-through control method for offshore wind farm ac asymmetric faults described above in the embodiments shown in fig. 1-5F. In detail, please refer to the multi-stage traversing control method of the ac asymmetric fault of the offshore wind farm in the embodiment shown in fig. 1-5F, which is not described herein.
The embodiment of the invention also provides a computer readable storage medium, on which the computer program is stored. The program, when executed by the processor, implements a multi-stage ride-through control method for an ac asymmetric fault of an offshore wind farm in the embodiments shown in fig. 1-5F, which is not described herein.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (10)

1. A multi-stage ride-through control method for an ac asymmetric fault of an offshore wind farm for a system comprising the offshore wind farm, an offshore converter station and an onshore ac grid, the method comprising:
when an alternating current asymmetric fault is detected to occur on the offshore side of the system, reactive compensation and current amplitude limiting control are carried out on the offshore wind farm;
starting sequence network energy control of the offshore converter station to inhibit a negative sequence current component under an alternating current asymmetric fault through positive and negative sequence decomposition control, and calculating an energy absorption slope of the first-stage sequence network energy control through active energy control; and controlling the offshore converter station to absorb the energy output by the offshore wind farm at a rate corresponding to the energy absorption slope;
when the AC asymmetric fault is detected to be cleared, calculating the energy release slope of the energy control of the second-stage sequence network through the active energy control, and controlling the offshore converter station to release energy to the onshore AC power network at the rate corresponding to the energy release slope.
2. A multi-stage ride-through control method of an ac asymmetry fault for an offshore wind farm according to claim 1, wherein when it is detected that the ac asymmetry fault is cleared, the method further comprises:
and calculating an outer ring voltage reference value through additional alternating voltage outer ring inhibition, and controlling the offshore converter station according to the outer ring voltage reference value so as to avoid overvoltage of an offshore grid-connected point.
3. The multi-stage ride-through control method of an ac asymmetric fault of an offshore wind farm according to claim 2, wherein the outer loop voltage reference value is:
U sdref2 ＝U sdref +K p (U sdref- U sdpu )
wherein ,Usdref 、U sdref2 Respectively the external ring voltage reference values before and after the external ring suppression of the additional alternating voltage, U sdpu Is the per unit value, K of the amplitude of the AC voltage at the grid-connected point p Is a compensation coefficient.
4. A multi-stage ride-through control method for ac asymmetric faults in an offshore wind farm as claimed in claim 1, characterised in that the reactive power compensation reference value Q of the offshore wind farm is used in reactive power compensation ref The method comprises the following steps:
i sqref ≥1.5×(0.9-U sd )I s
wherein ,Usd D-axis component of offshore grid-tie voltage for incorporation of offshore wind farms into offshore converter stations, I s Output current amplitude, i, for offshore wind farm sdref 、i sqref Reference values i of current inner ring d and q axis currents of offshore wind power plant respectively smax The maximum amplitude of the current output by the ring of the offshore wind farm is set; according to i smax And performing current limiting control.
5. A multi-phase ride-through control method for an ac asymmetric fault in an offshore wind farm as claimed in any of claims 1 to 4, wherein the energy absorption slope is:
wherein ,k1 For the energy absorption slope, P s For real-time power value, P, output by offshore wind farm acmax Maximum value of alternating current power output to offshore converter station for offshore wind farm, P dc Real-time DC power, deltaW, for an offshore wind farm to be output to an offshore converter station WFMMC For varying the energy value of the offshore converter station, U sj1 、U sj2 J-phase sampling values of the offshore grid-connected voltage before and after a fault sampling period respectively, wherein DeltaT is a fault sampling period and W is a fault sampling period WFMMCmax For the maximum upper limit of the energy of the offshore converter station, U sjmax Maximum values are allowed for j phase shunt voltage operation, j=a, b, c.
6. A multi-phase ride-through control method for an ac asymmetric fault in an offshore wind farm as claimed in claim 5, wherein the energy variation relationship of the offshore converter station during the energy control of the first phase sequence network is:
wherein ,is equivalent electromotive force of WFMMC side, +.>Is equivalent to grid connection after the sub-module is input due to the energy control of the first-stage gridVoltage, Z MMC Equivalent reactance of MMC side, +.>For MMC side alternating current, +.>For the fault voltage formed at the fault point, W MMC For real-time value of converter station energy, C arm For the average value of the submodule capacitance,/->Sub-module voltage average values P of upper bridge arm and lower bridge arm of j phases respectively ac Real-time ac power output to an offshore converter station for an offshore wind farm, U dc 、I dc The DC voltage value and the DC current value of the offshore DC submarine cable are respectively set.
7. A multi-phase ride-through control method for an ac asymmetric fault in an offshore wind farm as claimed in any of claims 1 to 4, wherein the energy release slope is:
wherein ,k2 For the energy release slope, S N For rated reference capacity of system, W WFMMC0 For steady state energy value, P, of an offshore converter station under nominal operating conditions dc 、P ac The real-time direct current power and the real-time alternating current power which are respectively output to the offshore converter station by the offshore wind farm.
8. A multi-stage ride-through control method of an ac asymmetry fault in an offshore wind farm according to claim 1, further comprising, prior to said initiating sequence grid energy control of the offshore converter station: the three-phase circuit parameters are converted into circuit parameters in a sequence network for calculating the energy absorption slope and the energy release slope.
9. A multi-stage ride-through control device for an ac asymmetric fault of an offshore wind farm for a system comprising the offshore wind farm, an offshore converter station and an onshore ac grid, the device comprising:
the compensation and amplitude limiting module is used for carrying out reactive compensation and current amplitude limiting control on the offshore wind farm when an alternating current asymmetric fault on the offshore side of the system is detected;
the first phase sequence network energy control module is used for starting sequence network energy control of the offshore converter station so as to inhibit a negative sequence current component under an alternating current asymmetric fault through positive and negative sequence decomposition control, and calculating an energy absorption slope of the first phase sequence network energy control through active energy control; and controlling the offshore converter station to absorb the energy output by the offshore wind farm at a rate corresponding to the energy absorption slope;
and the second-stage sequence network energy control module is used for calculating the energy release slope of the second-stage sequence network energy control through the active energy control when the AC asymmetric fault is detected to be cleared, and controlling the offshore converter station to release energy to the onshore AC power grid at the rate corresponding to the energy release slope.
10. A computer readable storage medium having stored thereon a computer program, wherein the program when executed by a processor implements a multi-stage ride-through control method of an offshore wind farm ac asymmetry fault according to any of claims 1-8.
CN202310585919.0A 2023-05-23 2023-05-23 Multi-stage traversing control method and device for alternating current asymmetric faults of offshore wind farm Pending CN116646953A (en)

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