CN115313488B - Impedance determination method and system for offshore wind power through soft direct grid connection system - Google Patents

Impedance determination method and system for offshore wind power through soft direct grid connection system Download PDF

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CN115313488B
CN115313488B CN202211019344.8A CN202211019344A CN115313488B CN 115313488 B CN115313488 B CN 115313488B CN 202211019344 A CN202211019344 A CN 202211019344A CN 115313488 B CN115313488 B CN 115313488B
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offshore
network side
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flexible
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CN115313488A (en
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宾子君
孔祥平
李鹏
张弛
袁宇波
高磊
周琦
郑俊超
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State Grid Jiangsu Electric Power Co Ltd
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/14—Fourier, Walsh or analogous domain transformations, e.g. Laplace, Hilbert, Karhunen-Loeve, transforms
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/16—Matrix or vector computation, e.g. matrix-matrix or matrix-vector multiplication, matrix factorization
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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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Abstract

The invention discloses a method for determining impedance of a soft direct grid-connected system of offshore wind power, which comprises the following steps: acquiring voltage and current waveforms of an offshore wind power plant to be analyzed and a flexible direct current converter station at each port; preprocessing waveforms under different working conditions, extracting resonant frequency components and carrying out phase sequence conversion; constructing a port circuit network equation of the offshore wind power soft and straight sending-out system under the resonance frequency; calculating the initial value of the port circuit network equation; and (5) iteratively solving a network equation under the resonance working condition to obtain the impedance of each wind field and the flexible system and the harmonic source parameters. According to the method, based on actual measurement recording data and by combining a window Fourier analysis and nonlinear circuit equation solving method, the impedance of the flexible direct system and the wind power plant under the resonance working condition is calculated quickly, compared with the existing method, the accuracy of broadband oscillation positioning and analysis of the offshore wind power via the flexible direct grid-connected system is improved greatly, and an analysis tool is provided for field debugging work of broadband oscillation.

Description

Impedance determination method and system for offshore wind power through soft direct grid connection system
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to a method and a system for determining impedance of a soft direct grid-connected system of offshore wind power.
Background
The offshore wind power generation system has the problem of complex broadband oscillation through the soft direct grid-connected system, related research is generally carried out on the basis of an offline small signal model or online impedance sweep frequency characteristics, however, the operation working conditions of the offshore wind power plant are numerous, the control strategy of a large number of power electronic devices in the soft direct system is complex, and the problems of inaccurate offline model and lack of analysis tools exist in the broadband oscillation research of an actual system. The method is characterized in that a fault scene is difficult to reproduce on an off-line platform after broadband oscillation occurs, and impedance characteristics of relevant frequency bands of the system are calculated, so that great inconvenience is brought to positioning of an oscillation source, and difficulty is brought to further analysis of broadband oscillation characteristics and oscillation suppression of the offshore wind power through a soft direct grid-connected system.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for determining the impedance of the offshore wind power soft direct grid-connected system, which can realize the calculation of the actual system harmonic impedance.
The technical problems to be solved by the invention are realized by the following technical scheme:
in a first aspect, a method for determining impedance of a soft direct grid-connected system of offshore wind power is provided, which is characterized by comprising the following steps:
Acquiring voltage and current waveforms of each port of the offshore wind farm and the soft direct current converter station under steady-state working conditions and resonance working conditions;
extracting resonant frequency components of each port voltage and current waveform under a steady-state working condition and a resonant working condition, and carrying out phase sequence conversion;
constructing a port circuit network equation of the offshore wind power soft and straight sending-out system according to the resonant frequency component after the phase sequence conversion;
estimating the initial value of a circuit network equation according to harmonic components of the voltage and the current of each port under a steady-state working condition;
substituting the initial value of the equation, and iteratively solving a positive and negative zero sequence component network equation under the resonance working condition to obtain positive and negative zero sequence impedance of each wind field and the flexible direct system under the resonance frequency.
With reference to the first aspect, further, the obtaining the voltage and current waveforms of each port of the offshore wind farm and the soft direct current converter station under the steady-state working condition and the resonance working condition includes:
acquiring three-phase voltage and current waveforms of a flexible-direct system offshore alternating current network side port from intra-station wave recording;
and acquiring three-phase voltage and current waveforms of the cross current network side port of the collection station of the offshore wind farm from the wave recording in the station.
With reference to the first aspect, further, the three-phase voltage and current waveforms of the offshore alternating current network side port of the flexible-direct system are expressed as:
U Sa (t)＝[U S1,a (t),U S2,a (t),…,U Sn,a (t)]
U Sb (t)＝[U S1,b (t),U S2,b (t),…,U Sn,b (t)]
U Sc (t)＝[U S1,c (t),U S2,c (t),…,U Sn,c (t)]
I Sa (t)＝[I S1,a (t),I S2,a (t),…,I Sn,a (t)]
I Sb (t)＝[I S1,b (t),I S2,b (t),…,I Sn,b (t)]
I Sc (t)＝[I S1,c (t),I S2,c (t),…,I Sn,c (t)]
Wherein U is Sa (t)、U Sb (t) and U Sc (t) is the voltages of a, b and c phases of the offshore alternating current network side of the flexible-direct system respectively, I Sa (t)、I Sb (t) and I Sc And (t) are the phase currents of the a, b and c sides of the offshore alternating current network of the flexible-direct system, and subscripts 1 to n respectively represent the 1 st to n th ports.
With reference to the first aspect, further, the three-phase voltage and current waveforms of the ac network side port of the offshore wind farm collection station are expressed as:
U a (t)＝[U 1,a (t),U 2,a (t),…,U m,a (t)]
U b (t)＝[U 1,b (t),U 2,b (t),…,U m,b (t)]
U c (t)＝[U 1,c (t),U 2,c (t),…,U m,c (t)]
I a (t)＝[I 1,a (t),I 2,a (t),…,I m,a (t)]
I b (t)＝[I 1,b (t),I 2,b (t),…,I m,b (t)]
I c (t)＝[I 1,c (t),I 2,c (t),…,I m,c (t)]
wherein U is a (t)、U b (t) and U c (t) is the phase voltages of a, b and c on the collecting station network side of the offshore wind farm respectively, I a (t)、I b (t) and I c And (t) respectively collecting phase currents of a station network side a, b and c of the offshore wind farm, wherein subscripts 1-m respectively represent 1-m ports.
With reference to the first aspect, further, extracting the resonant frequency components of the voltage and current waveforms of each port under the steady-state working condition and the resonant working condition and performing phase sequence transformation includes:
the voltage and current waveform pairs of different ports are paired based on the GPS time signal of the oscillograph;
selecting the time under the resonance working conditionDiscontinuities t h At f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] h -1/(2Δf),t h +1/(2Δf)]Wherein f S The sampling frequency of the original signal is shown as delta f, and the spectrum resolution is shown as delta f; the electric quantity of the soft-direct system offshore alternating current network side port and the offshore wind farm collecting station network side port are windowed to obtain Fourier transform to obtain a soft-direct system offshore alternating current network side a, b and c phase voltage Fourier spectrum M USa (f h )、M USb (f h ) And M is as follows USc (f h ) Obtaining a Fourier spectrum M of a, b and c phase currents of the flexible-direct system offshore alternating current network side ISa (f h )、M ISb (f h ) And M is as follows ISc (f h ) Phase a, b and c voltage Fourier spectrum M of collection station network side of offshore wind farm Ua (f h )、M Ub (f h ) And M is as follows Uc (f h ) Phase a, b and c current Fourier spectrum M of offshore wind farm network side collection station Ia (f h )、M Ib (f h ) And M is as follows Ic (f h )；
Phase sequence transformation is carried out on electric quantity resonance frequency components of each port based on phase sequence transformation matrix D
The phase sequence transformation moment D is shown below
The phase sequence transformation is as follows:
[M US1 (f h ),M US2 (f h ),M US0 (f h )] T ＝D[M USa (f h ),M USb (f h ),M USc (f h )] T
[M IS1 (f h ),M IS2 (f h ),M IS0 (f h )] T ＝D[M ISa (f h ),M ISb (f h ),M ISc (f h )] T
[M U1 (f h ),M U2 (f h ),M U0 (f h )] T ＝D[M Ua (f h ),M Ub (f h ),M Uc (f h )] T
[M I1 (f h ),M I2 (f h ),M I0 (f h )] T ＝D[M Ia (f h ),M Ib (f h ),M Ic (f h )] T
wherein M is US1 (f h )、M US2 (f h )、M US0 (f h ) The positive sequence, negative sequence and zero sequence components of the port voltage of the offshore alternating current network side of the flexible direct current system in the complex expression form at the resonant frequency; m is M IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; the method comprises the steps of carrying out a first treatment on the surface of the M is M U1 (f h )、M U2 (f h )、M U0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; m is M I1 (f h )、M I2 (f h )、M I0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of station network side port current at resonant frequency for a complex expression form of the offshore wind farm;
selecting a time section t under a steady-state working condition o And t is equal to h With an interval of 1/f h Integer multiple of f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] o -1/(2Δf),t o +1/(2Δf)]The electric quantity of the port on the side of the offshore alternating current network of the flexible direct system and the electric quantity of the port on the side of the collecting station network of the offshore wind farm are windowed to obtain Fourier transform, and a phase voltage Fourier spectrum of a, b and c of the offshore alternating current network of the flexible direct system is obtained And->Obtaining a Fourier spectrum of a, b and c phase currents at the offshore alternating current network side of the flexible-direct system/>And->Obtaining a Fourier spectrum of phase voltages of a, b and c at the collecting station network side of the offshore wind farm +.>And->Similarly, a Fourier spectrum of the current of phases a, b and c on the net side of the collection station of the offshore wind farm is obtained>And->
The phase sequence transformation of the electric quantity resonance frequency components of each port is as follows:
wherein,flexible and straight system in plural expression formPositive sequence, negative sequence and zero sequence components of the port voltage of the offshore alternating current network side at the resonant frequency; />The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; />The current of the port of the station network side is collected for the complex expression type offshore wind farm in the positive sequence, the negative sequence and the zero sequence components of the resonant frequency.
With reference to the first aspect, further, the constructing a port circuit network equation of the offshore wind power via flexible straight delivery system includes:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind farms to a harmonic current source i Vi And harmonic impedance z Vi In parallel, wherein subscript i is the wind farm number; equating the side ports of the offshore alternating current network of the n flexible-direct system as a harmonic voltage source u Mj And z Mj The harmonic impedance is in a series connection form, wherein the subscript j is the serial number of a port on a soft and straight rectifying side;
aiming at the topological structure of the actual system before resonance, a circuit network equation is written according to the kirchhoff current and voltage law;
for positive sequence network Y 1 ＝F 1 (X 1 )，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity to formIs a function value, where u 1,1 (f h ),…,u m,1 (f h ) And u is equal to S1,1 (f h ),…,u Sn,1 (f h ) The positive sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th flexible-direct-system offshore alternating-current network side ports are respectively 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) The system comprises a 1 st to m seaborne wind power plant collection station network side port positive sequence harmonic current component source and a 1 st to n soft direct system seaborne alternating current network side port positive sequence harmonic current component; each positive sequence impedance component to be solvedAs an unknown variable, where z V1,1 (f h ),…,z Vm,1 (f h ) And z M1,1 (f h ),…,z Mn,1 (f h ) Equivalent positive sequence impedance of 1 st to m seaborne wind power plant collecting station network side ports and 1 st to n soft and straight system seaborne alternating current network side ports, i V1,1 (f h ),…,i Vm,1 (f h ) And u is equal to M1,1 (f h ),…,u Mn,1 (f h ) The method comprises the steps of respectively providing 1 st to m equivalent positive sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent positive sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible and straight system;
For negative sequence network Y 2 ＝F 2 (X 2 )，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity to formIs a function value, where u 1,2 (f h ),…,u m,2 (f h ) And u is equal to S1,2 (f h ),…,u Sn,2 (f h ) Respectively the 1 st to m th offshore wind farm collecting station network side ports and the 1 st to n th soft-direct system offshore alternating current network side ports negative sequence harmonic voltage components, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) 1 st to m th offshore wind powerA field collection station network side port negative sequence harmonic current component source and 1 st to nth soft-direct system offshore alternating current network side port negative sequence harmonic current components; each negative sequence impedance composition to be solvedAs an unknown variable, where z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Respectively equivalent negative sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,2 (f h ),…,i Vm,2 (f h ) And u is equal to M1,2 (f h ),…,u Mn,2 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent negative sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent negative sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system;
for zero sequence network Y 0 ＝F 0 (X 0 )，F 0 For nonlinear circuit equation, selecting zero sequence component composition of electric quantityIs a function value, where u 1,0 (f h ),…,u m,0 (f h ) And u is equal to S1,0 (f h ),…,u Sn,0 (f h ) The zero sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th soft-direct system offshore alternating current network side ports are respectively 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) The method comprises the steps of collecting a station network side port zero-sequence harmonic current component source of a 1 st to m th offshore wind farm and a 1 st to n th offshore alternating current network side port zero-sequence harmonic current component of a flexible direct system respectively; each zero sequence impedance component to be solved As an unknown variable, where z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Equivalent zero sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,0 (f h ),…,i Vm,0 (f h ) And u is equal to M1,0 (f h ),…,u Mn,0 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent zero sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent zero sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system.
With reference to the first aspect, further, the estimating the initial value of the circuit network equation according to the harmonic component of each port voltage and each port current under the steady-state working condition includes:
for an actual system topological structure before resonance, substituting harmonic components of current of a collection station port of an offshore wind farm under normal working conditions into the actual system topological structure to serve as an equivalent harmonic current source of the collection station port of the offshore wind farm, taking harmonic components of voltage of a flexible-direct system offshore alternating current network side port under steady-state working conditions into an equivalent harmonic voltage source of the flexible-direct system offshore alternating current network side port, and enabling
Based on kirchhoff current and voltage law, the circuit is written with positive sequence, negative sequence and zero sequence network equationY 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F is equal to 0 (o) Is a nonlinear circuit equation +.>And (3) withFor the function value of the function, and (3) withIs an unknown variable;
X 1 (o) 、X 2 (o) and X is 0 (o) Adopting typical impedance characteristic parameters of a wind power plant and a flexible-direct system as initial values, and solving a nonlinear equation set Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) ) The result of the solution is marked as X 1 (1) 、X 2 (1) And X is 0 (1) 。
In combination with the first aspect, the process of obtaining the positive and negative zero sequence impedance of each wind field and the flexible system is as follows:
for circuit network equation Y 1 ＝F 1 (X 1 )、Y 2 ＝F 2 (X 2 ) And Y is equal to 0 ＝F 0 (X 0 ) Let the initial values be respectively
And (3) with
Iterative solving equation based on numerical method to obtain each harmonic source to be solved and positive sequence complex impedance value X 1 、X 2 And X is 0 。
In a second aspect, a method for determining impedance of a soft direct grid-connected system of offshore wind power is provided, which comprises the following steps:
the voltage and current waveform acquisition module is used for acquiring voltage and current waveforms of each port of the offshore wind power plant and the flexible direct current converter station under steady-state working conditions and resonance working conditions;
the phase sequence conversion module is used for extracting resonant frequency components of each port voltage and current waveform under the steady-state working condition and the resonance working condition and carrying out phase sequence conversion;
the equation construction module is used for constructing a port circuit network equation of the offshore wind power system which is sent out from the system through flexible straight according to the resonant frequency component after the phase sequence conversion;
the equation initial value calculation module is used for estimating a circuit network equation initial value according to harmonic components of the voltage and the current of each port under the steady-state working condition;
and the impedance calculation module is used for substituting the initial value of the equation, and iteratively solving the positive and negative zero sequence component network equation under the resonance working condition to obtain the positive and negative zero sequence impedance of each wind field and the flexible direct system under the resonance frequency.
With reference to the second aspect, further operations performed by the voltage-current waveform acquisition module include:
acquiring three-phase voltage and current waveforms of a flexible-direct system offshore alternating current network side port from intra-station wave recording;
and acquiring three-phase voltage and current waveforms of the cross current network side port of the collection station of the offshore wind farm from the wave recording in the station.
With reference to the second aspect, further, the three-phase voltage and current waveforms of the offshore alternating current network side port of the flexible-direct system are expressed as:
U Sa (t)＝[U S1,a (t),U S2,a (t),…,U Sn,a (t)]
U Sb (t)＝[U S1,b (t),U S2,b (t),…,U Sn,b (t)]
U Sc (t)＝[U S1,c (t),U S2,c (t),…,U Sn,c (t)]
I Sa (t)＝[I S1,a (t),I S2,a (t),…,I Sn,a (t)]
I Sb (t)＝[I S1,b (t),I S2,b (t),…,I Sn,b (t)]
I Sc (t)＝[I S1,c (t),I S2,c (t),…,I Sn,c (t)]
wherein U is Sa (t)、U Sb (t) and U Sc (t) is the voltages of a, b and c phases of the offshore alternating current network side of the flexible-direct system respectively, I Sa (t)、I Sb (t) and I Sc And (t) are the phase currents of the a, b and c sides of the offshore alternating current network of the flexible-direct system, and subscripts 1 to n respectively represent the 1 st to n th ports.
With reference to the second aspect, further, the three-phase voltage and current waveforms of the ac network side port of the offshore wind farm collection station are expressed as:
U a (t)＝[U 1,a (t),U 2,a (t),…,U m,a (t)]
U b (t)＝[U 1,b (t),U 2,b (t),…,U m,b (t)]
U c (t)＝[U 1,c (t),U 2,c (t),…,U m,c (t)]
I a (t)＝[I 1,a (t),I 2,a (t),…,I m,a (t)]
I b (t)＝[I 1,b (t),I 2,b (t),…,I m,b (t)]
I c (t)＝[I 1,c (t),I 2,c (t),…,I m,c (t)]
wherein U is a (t)、U b (t) and U c (t) is the phase voltages of a, b and c on the collecting station network side of the offshore wind farm respectively, I a (t)、I b (t) and I c And (t) are the current of the a, b and c phases of the offshore wind farm network side, and subscripts 1-m respectively represent 1-m ports.
With reference to the second aspect, further operations performed by the phase sequence transformation module include:
the voltage and current waveform pairs of different ports are paired based on the GPS time signal of the oscillograph;
Selecting a time section t under a resonance working condition h At f S And/. DELTA.f isAnalysis window construction square wave signal window function g (t) =1, t= [ t ] h -1/(2Δf),t h +1/(2Δf)]Wherein f S The sampling frequency of the original signal is shown as delta f, and the spectrum resolution is shown as delta f; the electric quantity of the soft-direct system offshore alternating current network side port and the offshore wind farm collecting station network side port are windowed to obtain Fourier transform to obtain a soft-direct system offshore alternating current network side a, b and c phase voltage Fourier spectrum M USa (f h )、M USb (f h ) And M is as follows USc (f h ) Obtaining a Fourier spectrum M of a, b and c phase currents of the flexible-direct system offshore alternating current network side ISa (f h )、M ISb (f h ) And M is as follows ISc (f h ) Phase a, b and c voltage Fourier spectrum M of collection station network side of offshore wind farm Ua (f h )、M Ub (f h ) And M is as follows Uc (f h ) Phase a, b and c current Fourier spectrum M at collection station network side of offshore wind farm Ia (f h )、M Ib (f h ) And M is as follows Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency components of each port based on a phase sequence transformation matrix D;
the phase sequence transformation moment D is as follows:
the phase sequence transformation is as follows:
[M US1 (f h ),M US2 (f h ),M US0 (f h )] T ＝D[M USa (f h ),M USb (f h ),M USc (f h )] T
[M IS1 (f h ),M IS2 (f h ),M IS0 (f h )] T ＝D[M ISa (f h ),M ISb (f h ),M ISc (f h )] T
[M U1 (f h ),M U2 (f h ),M U0 (f h )] T ＝D[M Ua (f h ),M Ub (f h ),M Uc (f h )] T
[M I1 (f h ),M I2 (f h ),M I0 (f h )] T ＝D[M Ia (f h ),M Ib (f h ),M Ic (f h )] T
wherein M is US1 (f h )、M US2 (f h )、M US0 (f h ) The port voltage of the soft direct system offshore alternating current network side in the complex expression form is positive sequence, negative sequence and zero sequence components of the resonant frequency; m is M IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; m is M U1 (f h )、M U2 (f h )、M U0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; m is M I1 (f h )、M I2 (f h )、M I0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of station network side port current at resonant frequency for a complex expression form of the offshore wind farm;
selecting a time section t under a steady-state working condition o And t is equal to h With an interval of 1/f h Integer multiple of f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] o -1/(2Δf),t o +1/(2Δf)]The electric quantity of the port on the side of the offshore alternating current network of the flexible direct system and the electric quantity of the port on the side of the collecting station network of the offshore wind farm are windowed to obtain Fourier transform, and a phase voltage Fourier spectrum of a, b and c of the offshore alternating current network of the flexible direct system is obtainedAnd->Obtaining a Fourier spectrum of a, b and c phase currents of the flexible-direct system offshore alternating current network side +.>And->Obtaining a Fourier spectrum of phase voltages of a, b and c at the collecting station network side of the offshore wind farm>And->Similarly, a Fourier spectrum of the current of phases a, b and c on the net side of the collection station of the offshore wind farm is obtained>And->
The phase sequence transformation of the electric quantity resonance frequency components of each port is as follows:
wherein,the positive sequence, negative sequence and zero sequence components of the port voltage of the offshore alternating current network side of the flexible direct current system in the complex expression form at the resonant frequency; />The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; / >The current of the port of the station network side is collected for the complex expression type offshore wind farm in the positive sequence, the negative sequence and the zero sequence components of the resonant frequency.
With reference to the second aspect, further operations performed by the equation construction module include:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind farms to a harmonic current source i Vi And harmonic impedance z Vi In parallel, wherein subscript i is the wind farm number; equating the side ports of the offshore alternating current network of the n flexible-direct system as a harmonic voltage source u Mj And z Mj The harmonic impedance is in a series connection form, wherein the subscript j is the port number of the offshore alternating current network side of the flexible-direct system;
aiming at the topological structure of the actual system before resonance, a circuit network equation is written according to the kirchhoff current and voltage law;
for positive sequence network Y 1 ＝F 1 (X 1 )，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity to formIs a function value, where u 1,1 (f h ),…,u m,1 (f h ) And u is equal to S1,1 (f h ),…,u Sn,1 (f h ) The positive sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th flexible-direct-system offshore alternating-current network side ports are respectively 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) The system comprises a 1 st to m seaborne wind power plant collection station network side port positive sequence harmonic current component source and a 1 st to n soft direct system seaborne alternating current network side port positive sequence harmonic current component; each positive sequence impedance component to be solved As an unknown variable, where z V1,1 (f h ),…,z Vm,1 (f h ) And z M1,1 (f h ),…,z Mn,1 (f h ) Equivalent positive sequence impedance of 1 st to m seaborne wind power plant collecting station network side ports and 1 st to n soft and straight system seaborne alternating current network side ports, i V1,1 (f h ),…,i Vm,1 (f h ) And u is equal to M1,1 (f h ),…,u Mn,1 (f h ) The method comprises the steps of respectively providing 1 st to m equivalent positive sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent positive sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible and straight system;
for negative sequence network Y 2 ＝F 2 (X 2 )，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity to formIs a function value, where u 1,2 (f h ),…,u m,2 (f h ) And u is equal to S1,2 (f h ),…,u Sn,2 (f h ) Respectively the 1 st to m th offshore wind farm collecting station network side ports and the 1 st to n th soft-direct system offshore alternating current network side ports negative sequence harmonic voltage components, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) The method comprises the steps of collecting a network side port negative sequence harmonic current component source of a station network of a 1 st to m-th offshore wind farm and a network side port negative sequence harmonic current component of a 1 st to n-th offshore alternating current network of a flexible and straight system respectively; each negative sequence impedance composition to be solvedAs an unknown variable, where z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Respectively equivalent negative sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,2 (f h ),…,i Vm,2 (f h ) And u is equal to M1,2 (f h ),…,u Mn,2 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent negative sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent negative sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system;
For zero sequence network Y 0 ＝F 0 (X 0 )，F 0 For nonlinear circuit equation, selecting zero sequence component composition of electric quantityIs a function value, where u 1,0 (f h ),…,u m,0 (f h ) And u is equal to S1,0 (f h ),…,u Sn,0 (f h ) The zero sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th soft-direct system offshore alternating current network side ports are respectively 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) The method comprises the steps of collecting a station network side port zero-sequence harmonic current component source of a 1 st to m th offshore wind farm and a 1 st to n th offshore alternating current network side port zero-sequence harmonic current component of a flexible direct system respectively; each zero sequence impedance component to be solvedAs an unknown variable, where z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Equivalent zero sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,0 (f h ),…,i Vm,0 (f h ) And u is equal to M1,0 (f h ),…,u Mn,0 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent zero sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent zero sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system.
With reference to the second aspect, further operations performed by the equation initial value calculation module include:
for an actual system topological structure before resonance, substituting harmonic components of current of a collection station port of an offshore wind farm under normal working conditions into the actual system topological structure to serve as an equivalent harmonic current source of the collection station port of the offshore wind farm, taking harmonic components of voltage of a flexible-direct system offshore alternating current network side port under steady-state working conditions into an equivalent harmonic voltage source of the flexible-direct system offshore alternating current network side port, and enabling
Based on kirchhoff current and voltage law, the circuit writes positive sequence, negative sequence and zero sequence network equation Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F is equal to 0 (o) Is a non-linear circuit equation,and (3) withFor the function value of the function, and (3) withIs an unknown variable;
X 1 (o) 、X 2 (o) and X is 0 (o) By wind power plant and softnessTaking a typical impedance characteristic parameter of a straight system as an initial value, and solving a nonlinear equation set Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) ) The result of the solution is marked as X 1 (1) 、X 2 (1) And X is 0 (1) 。
The beneficial effects are that: according to the invention, an electric quantity list is written into an electric network equation according to actual measurement under harmonic frequencies of all ports when broadband oscillation occurs; constructing a nonlinear equation set between port voltage and current and harmonic current/voltage source and equivalent impedance of the offshore wind power through a soft direct grid-connected system; and reasonably setting an initial value of equivalent impedance of the offshore wind power plant and the flexible-straight system, and carrying out iterative solution on the equation to realize calculation and analysis of the harmonic impedance characteristics of the actual system.
Drawings
FIG. 1 is a flow chart of a method for determining impedance of an offshore wind power grid-connected system through soft and direct connection.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Example 1
As shown in fig. 1, the invention provides a method for determining the impedance of an offshore wind power grid-connected system through soft and direct connection,
step one, acquiring voltage and current waveforms of each port of the offshore wind power plant to be analyzed and the flexible direct current converter station under steady-state working condition and resonance working condition.
For the offshore wind power with m wind farms and n soft and straight rectification ports, acquiring three-phase voltage and current waveforms of the ports of the offshore alternating current network side of the soft and straight system from the wave recording in the station through the soft and straight grid-connected system, and marking as follows:
U Sa (t)＝[U S1,a (t),U S2,a (t),…,U Sn,a (t)]
U Sb (t)＝[U S1,b (t),U S2,b (t),…,U Sn,b (t)]
U Sc (t)＝[U S1,c (t),U S2,c (t),…,U Sn,c (t)]
I Sa (t)＝[I S1,a (t),I S2,a (t),…,I Sn,a (t)]
I Sb (t)＝[I S1,b (t),I S2,b (t),…,I Sn,b (t)]
I Sc (t)＝[I S1,c (t),I S2,c (t),…,I Sn,c (t)]
wherein U is Sa (t)、U Sb (t) and U Sc (t) is the voltages of a, b and c phases of the offshore alternating current network side of the flexible-direct system respectively, I Sa (t)、I Sb (t) and I Sc And (t) are the phase currents of the a, b and c sides of the offshore alternating current network of the flexible-direct system, and subscripts 1 to n respectively represent the 1 st to n th ports.
Acquiring three-phase voltage and current waveforms of a cross current network side port of a collection station of the offshore wind farm from the wave recording in the station, and recording the three-phase voltage and current waveforms as follows:
U a (t)＝[U 1,a (t),U 2,a (t),…,U n,a (t)]
U b (t)＝[U 1,b (t),U 2,b (t),…,U n,b (t)]
U c (t)＝[U 1,c (t),U 2,c (t),…,U n,c (t)]
I a (t)＝[I 1,a (t),I 2,a (t),…,I n,a (t)]
I b (t)＝[I 1,b (t),I 2,b (t),…,I n,b (t)]
I c (t)＝[I 1,c (t),I 2,c (t),…,I n,c (t)]
wherein U is a (t)、U b (t) and U c (t) is the voltages of a, b and c phases at the sea wind field net side respectively, I a (t)、I b (t) and I c And (t) are the current of the a, b and c phases of the offshore wind farm network side, and subscripts 1-m respectively represent 1-m ports.
And step two, preprocessing port voltage and current waveforms under different working conditions (steady-state working condition and resonance working condition), extracting resonance frequency components and carrying out phase sequence conversion. The method specifically comprises the following steps:
s1, voltage and current waveform pairs of different ports are paired based on a recorder GPS time signal;
s2, selecting a time section t under a resonance working condition h At f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] h -1/(2Δf),t h +1/(2Δf)]Wherein f S For the original signal sampling frequency, Δf is the spectral resolution. The electric quantity of the soft direct system offshore alternating current network side port and the electric quantity of the offshore wind farm collecting station network side port are windowed to obtain Fourier transform, and a phase voltage Fourier spectrum of a, b and c of the soft direct system offshore alternating current network side is obtainedAnd->Obtaining a Fourier spectrum of a, b and c phase currents of the flexible-direct system offshore alternating current network side +.>And->Fourier spectrum of phase a, b and c voltages at collecting station network side of offshore wind farm +.>And->Obtaining Fourier spectrums of currents of phases a, b and c on the collecting station network side of the offshore wind farm +.>And->Subscripts 1 to n represent 1 st to n th ports, respectively; likewise, the Fourier spectrum M of the current of the a, b and c phases of the wind field network side can be obtained Ia (f h )、M Ib (f h ) And M is as follows Ic (f h ) Subscripts 1-m represent 1-m ports, respectively. />
S3, carrying out phase sequence conversion on the electric quantity resonance frequency components of each port based on the phase sequence conversion moment D
The phase sequence transformation moment D is shown below
The method comprises the following steps:
[M US1 (f h ),M US2 (f h ),M US0 (f h )] T ＝D[M USa (f h ),M USb (f h ),M USc (f h )] T
[M IS1 (f h ),M IS2 (f h ),M IS0 (f h )] T ＝D[M ISa (f h ),M ISb (f h ),M ISc (f h )] T
[M U1 (f h ),M U2 (f h ),M U0 (f h )] T ＝D[M Ua (f h ),M Ub (f h ),M Uc (f h )] T
[M I1 (f h ),M I2 (f h ),M I0 (f h )] T ＝D[M Ia (f h ),M Ib (f h ),M Ic (f h )] T
wherein,positive sequence, negative sequence and current of each port voltage and current at resonance frequency of flexible direct system offshore alternating current network in complex expression form
A zero sequence component;
the positive sequence, the negative sequence and the zero sequence components of the voltages and the currents of all ports on the collecting station network side of the offshore wind farm in the complex expression form are respectively in the resonance frequency.
S4, selecting a time section t under a steady-state working condition o And t is equal to h With an interval of 1/f h Integer multiple of f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] o -1/(2Δf),t o +1/(2Δf)]The electric quantity of the ports on the side of the offshore alternating current network of the flexible direct system and the ports on the side of the collecting station network of the offshore wind farm are windowed to obtain Fourier transform, and a phase current Fourier spectrum of a, b and c of the offshore alternating current network of the flexible direct system is obtainedAnd->Obtaining a Fourier spectrum of a, b and c phase currents of the flexible-direct system offshore alternating current network side +.>And->Obtaining a Fourier spectrum of phase voltages of a, b and c at the collecting station network side of the offshore wind farm +.>And->Subscripts 1 to n represent 1 to n ports, respectively; similarly, a Fourier spectrum of the current of phases a, b and c on the net side of the collection station of the offshore wind farm is obtained>And->Subscripts 1-m represent 1-m ports, respectively. />
The phase sequence transformation of the electric quantity resonance frequency components of each port is as follows:
wherein,the positive sequence, negative sequence and zero sequence components of the voltages and currents of all ports on the offshore alternating current network side of the flexible direct system in a complex expression form are respectively represented at the resonance frequency; />
The positive sequence, the negative sequence and the zero sequence components of the voltages and the currents of all ports on the collecting station network side of the offshore wind farm in the complex expression form are respectively in the resonance frequency.
And thirdly, constructing a port circuit network equation of the offshore wind power system which is sent out through the flexible direct transmission.
Aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind farms to a harmonic current source i Vi And harmonic impedance z Vi In parallel, wherein subscript i is the wind farm number; equating the side ports of the offshore alternating current network of the n flexible-direct system as a harmonic voltage source u Mj And z Mj The harmonic impedance is in series connection, wherein the subscript j is the port number of the offshore alternating current network side of the flexible-direct system.
Aiming at the actual system topological structure before resonance, a circuit network equation is written according to kirchhoff current and voltage law.
For positive sequence network Y 1 ＝F 1 (X 1 )，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity to formIs a function value, where u 1,1 (f h ),…,u m,1 (f h ) And u is equal to S1,1 (f h ),…,u Sn,1 (f h ) The positive sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th flexible-direct-system offshore alternating-current network side ports are respectively 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) The system comprises a 1 st to m seaborne wind power plant collection station network side port positive sequence harmonic current component source and a 1 st to n soft direct system seaborne alternating current network side port positive sequence harmonic current component; each positive sequence impedance component to be solvedAs an unknown variable, where z V1,1 (f h ),…,z Vm,1 (f h ) And z M1,1 (f h ),…,z Mn,1 (f h ) Equivalent positive sequence impedance of 1 st to m th ports of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible and straight system at collecting station network side respectively, i V1,1 (f h ),…,i Vm,1 (f h ) And u is equal to M1,1 (f h ),…,u Mn,1 (f h ) The method is characterized by comprising the step of respectively obtaining 1 st to m equivalent positive sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent positive sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible and straight system.
For negative sequence network Y 2 ＝F 2 (X 2 )，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity to formIs a function value, where u 1,2 (f h ),…,u m,2 (f h ) And u is equal to S1,2 (f h ),…,u Sn,2 (f h ) Respectively 1 st to m thNegative sequence harmonic voltage components of network side ports of collection stations of offshore wind farm and 1 st to nth soft and straight system offshore alternating current network side ports, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) The method comprises the steps of collecting a network side port negative sequence harmonic current component source of a station network of a 1 st to m-th offshore wind farm and a network side port negative sequence harmonic current component of a 1 st to n-th offshore alternating current network of a flexible and straight system respectively; the negative sequence impedance composition of each request>As an unknown variable, where z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Respectively equivalent negative sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,2 (f h ),…,i Vm,2 (f h ) And u is equal to M1,2 (f h ),…,u Mn,2 (f h ) The method is characterized by comprising the step of respectively obtaining 1 st to m offshore wind farm collection station port equivalent negative sequence harmonic current sources and 1 st to n soft-direct system offshore alternating current network side port equivalent negative sequence harmonic voltage sources.
For zero sequence network Y 0 ＝F 0 (X 0 )，F 0 For nonlinear circuit equation, selecting zero sequence component composition of electric quantityIs a function value, where u 1,0 (f h ),…,u m,0 (f h ) And u is equal to S1,0 (f h ),…,u Sn,0 (f h ) The zero sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th soft-direct system offshore alternating current network side ports are respectively 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) The method comprises the steps of collecting a station network side port zero-sequence harmonic current component source of a 1 st to m th offshore wind farm and a 1 st to n th offshore alternating current network side port zero-sequence harmonic current component of a flexible direct system respectively; each of which is provided withZero sequence impedance composition to be solvedAs an unknown variable, where z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Equivalent zero sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,0 (f h ),…,i Vm,0 (f h ) And u is equal to M1,0 (f h ),…,u Mn,0 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent zero sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent zero sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system.
Step four, calculating the initial value of a port circuit network equation based on harmonic components of each port voltage and current under normal working conditions, including:
s1, substituting harmonic components of current of a collection station port of an offshore wind farm under normal working conditions into an actual system topological structure before resonance to serve as an equivalent harmonic current source of the collection station port of the offshore wind farm, taking harmonic components of voltage of a flexible-direct system offshore alternating current network side port under steady-state working conditions as an equivalent harmonic voltage source of the flexible-direct system offshore alternating current network side port, and enabling
Based on kirchhoff current and voltage law, the circuit writes positive sequence, negative sequence and zero sequence network equation Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F is equal to 0 (o) Is a non-linear circuit equation,and (3) withFor the function value of the function, and (3) withIs an unknown variable.
S2，X 1 (o) 、X 2 (o) And X is 0 (o) Adopting a wind power plant and a flexible-direct system typical impedance characteristic parameter as an initial value, and solving a nonlinear equation set Y based on a least square method 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) ) The result of the solution is marked as X 1 (1) 、X 2 (1) And X is 0 (1) 。
And fifthly, substituting an equation initial value, and iteratively solving a positive and negative zero sequence component network equation under a resonance working condition to obtain positive and negative zero sequence impedance of each wind field and the flexible direct system under the resonance frequency.
For circuit network equation Y 1 ＝F 1 (X 1 )、Y 2 ＝F 2 (X 2 ) And Y is equal to 0 ＝F 0 (X 0 ) Let the initial values be respectively
And (3) with
Iterative solving equation based on numerical method to obtain each harmonic source to be solved and positive sequence complex impedance value X 1 、X 2 And X is 0 。
Example 2
The invention also provides an impedance determining system of the offshore wind power through-flexible direct grid-connected system, which comprises the following components:
the voltage and current waveform acquisition module is used for acquiring voltage and current waveforms of each port of the offshore wind power plant and the flexible direct current converter station under steady-state working conditions and resonance working conditions;
the phase sequence conversion module is used for extracting resonant frequency components of each port voltage and current waveform under the steady-state working condition and the resonance working condition and carrying out phase sequence conversion;
The equation construction module is used for constructing a port circuit network equation of the offshore wind power system which is sent out from the system through flexible straight according to the resonant frequency component after the phase sequence conversion;
the equation initial value calculation module is used for estimating a circuit network equation initial value according to harmonic components of the voltage and the current of each port under the steady-state working condition;
and the impedance calculation module is used for substituting the initial value of the equation, and iteratively solving the positive and negative zero sequence component network equation under the resonance working condition to obtain the positive and negative zero sequence impedance of each wind field and the flexible direct system under the resonance frequency.
The operation executed by the voltage and current waveform acquisition module comprises the following steps:
acquiring three-phase voltage and current waveforms of a flexible-direct system offshore alternating current network side port from intra-station wave recording;
and acquiring three-phase voltage and current waveforms of the cross current network side port of the collection station of the offshore wind farm from the wave recording in the station.
The operations performed by the phase sequence transformation module include:
the voltage and current waveform pairs of different ports are paired based on the GPS time signal of the oscillograph;
selecting a time section t under a resonance working condition h At f S The delta f is analysis window to construct square waveSignal window function g (t) =1, t= [ t ] h -1/(2Δf),t h +1/(2Δf)]Wherein f S The sampling frequency of the original signal is shown as delta f, and the spectrum resolution is shown as delta f; the electric quantity of the soft-direct system offshore alternating current network side port and the offshore wind farm collecting station network side port are windowed to obtain Fourier transform to obtain a soft-direct system offshore alternating current network side a, b and c phase voltage Fourier spectrum M USa (f h )、M USb (f h ) And M is as follows USc (f h ) Obtaining a Fourier spectrum M of a, b and c phase currents of the flexible-direct system offshore alternating current network side ISa (f h )、M ISb (f h ) And M is as follows ISc (f h ) Phase a, b and c voltage Fourier spectrum M of collection station network side of offshore wind farm Ua (f h )、M Ub (f h ) And M is as follows Uc (f h ) Phase a, b and c current Fourier spectrum M at collection station network side of offshore wind farm Ia (f h )、M Ib (f h ) And M is as follows Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency components of each port based on a phase sequence transformation matrix D;
the phase sequence transformation moment D is as follows:
the phase sequence transformation is as follows:
[M US1 (f h ),M US2 (f h ),M US0 (f h )] T ＝D[M USa (f h ),M USb (f h ),M USc (f h )] T
[M IS1 (f h ),M IS2 (f h ),M IS0 (f h )] T ＝D[M ISa (f h ),M ISb (f h ),M ISc (f h )] T
[M U1 (f h ),M U2 (f h ),M U0 (f h )] T ＝D[M Ua (f h ),M Ub (f h ),M Uc (f h )] T
[M I1 (f h ),M I2 (f h ),M I0 (f h )] T ＝D[M Ia (f h ),M Ib (f h ),M Ic (f h )] T
wherein M is US1 (f h )、M US2 (f h )、M US0 (f h ) The port voltage of the soft direct system offshore alternating current network side in the complex expression form is positive sequence, negative sequence and zero sequence components of the resonant frequency; m is M IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; m is M U1 (f h )、M U2 (f h )、M U0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; m is M I1 (f h )、M I2 (f h )、M I0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of station network side port current at resonant frequency for a complex expression form of the offshore wind farm;
selecting a time section t under a steady-state working condition o And t is equal to h With an interval of 1/f h Integer multiple of f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] o -1/(2Δf),t o +1/(2Δf)]The electric quantity of the port on the side of the offshore alternating current network of the flexible direct system and the electric quantity of the port on the side of the collecting station network of the offshore wind farm are windowed to obtain Fourier transform, and a phase voltage Fourier spectrum of a, b and c of the offshore alternating current network of the flexible direct system is obtained And->Obtaining a Fourier spectrum of a, b and c phase currents of the flexible-direct system offshore alternating current network side +.>And->Obtaining a Fourier spectrum of phase voltages of a, b and c at the collecting station network side of the offshore wind farm>And->Similarly, a Fourier spectrum of the current of phases a, b and c on the net side of the collection station of the offshore wind farm is obtained>And->
The phase sequence transformation of the electric quantity resonance frequency components of each port is as follows:
/>
wherein,the positive sequence, negative sequence and zero sequence components of the port voltage of the offshore alternating current network side of the flexible direct current system in the complex expression form at the resonant frequency; />In the form of complex expressionThe current of the port of the offshore alternating current network side of the flexible-direct system has positive sequence, negative sequence and zero sequence components at the resonant frequency; collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; />The current of the port of the station network side is collected for the complex expression type offshore wind farm in the positive sequence, the negative sequence and the zero sequence components of the resonant frequency.
The operations performed by the equation construction module include:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind farms to a harmonic current source i Vi And harmonic impedance z Vi In parallel, wherein subscript i is the wind farm number; equating the side ports of the offshore alternating current network of the n flexible-direct system as a harmonic voltage source u Mj And z Mj The harmonic impedance is in a series connection form, wherein the subscript j is the port number of the offshore alternating current network side of the flexible-direct system;
aiming at the topological structure of the actual system before resonance, a circuit network equation is written according to the kirchhoff current and voltage law;
for positive sequence network Y 1 ＝F 1 (X 1 )，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity to formIs a function value, where u 1,1 (f h ),…,u m,1 (f h ) And u is equal to S1,1 (f h ),…,u Sn,1 (f h ) The positive sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th flexible-direct-system offshore alternating-current network side ports are respectively 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) The system comprises a 1 st to m seaborne wind power plant collection station network side port positive sequence harmonic current component source and a 1 st to n soft direct system seaborne alternating current network side port positive sequence harmonic current component; each positive sequence impedance component to be solvedAs an unknown variable, where z V1,1 (f h ),…,z Vm,1 (f h ) And z M1,1 (f h ),…,z Mn,1 (f h ) Equivalent positive sequence impedance of 1 st to m seaborne wind power plant collecting station network side ports and 1 st to n soft and straight system seaborne alternating current network side ports, i V1,1 (f h ),…,i Vm,1 (f h ) And u is equal to M1,1 (f h ),…,u Mn,1 (f h ) The method comprises the steps of respectively providing 1 st to m equivalent positive sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent positive sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible and straight system;
for negative sequence network Y 2 ＝F 2 (X 2 )，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity to form Is a function value, where u 1,2 (f h ),…,u m,2 (f h ) And u is equal to S1,2 (f h ),…,u Sn,2 (f h ) Respectively the 1 st to m th offshore wind farm collecting station network side ports and the 1 st to n th soft-direct system offshore alternating current network side ports negative sequence harmonic voltage components, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) The method comprises the steps of collecting a network side port negative sequence harmonic current component source of a station network of a 1 st to m-th offshore wind farm and a network side port negative sequence harmonic current component of a 1 st to n-th offshore alternating current network of a flexible and straight system respectively; each negative sequence impedance composition to be solvedIs unknown toVariable, z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Respectively equivalent negative sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,2 (f h ),…,i Vm,2 (f h ) And u is equal to M1,2 (f h ),…,u Mn,2 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent negative sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent negative sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system;
for zero sequence network Y 0 ＝F 0 (X 0 )，F 0 For nonlinear circuit equation, selecting zero sequence component composition of electric quantityIs a function value, where u 1,0 (f h ),…,u m,0 (f h ) And u is equal to S1,0 (f h ),…,u Sn,0 (f h ) The zero sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th soft-direct system offshore alternating current network side ports are respectively 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) The method comprises the steps of collecting a station network side port zero-sequence harmonic current component source of a 1 st to m th offshore wind farm and a 1 st to n th offshore alternating current network side port zero-sequence harmonic current component of a flexible direct system respectively; each zero sequence impedance component to be solved As an unknown variable, where z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Equivalent zero sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,0 (f h ),…,i Vm,0 (f h ) And u is equal to M1,0 (f h ),…,u Mn,0 (f h ) Respectively are provided withThe method comprises the steps of providing equivalent zero sequence harmonic current sources at ports of collecting stations of 1 st to m th offshore wind power stations and equivalent zero sequence harmonic voltage sources at ports of offshore alternating current networks of 1 st to n th flexible-direct systems.
The operation executed by the equation initial value calculation module comprises the following steps:
for an actual system topological structure before resonance, substituting harmonic components of current of a collection station port of an offshore wind farm under normal working conditions into the actual system topological structure to serve as an equivalent harmonic current source of the collection station port of the offshore wind farm, taking harmonic components of voltage of a flexible-direct system offshore alternating current network side port under steady-state working conditions into an equivalent harmonic voltage source of the flexible-direct system offshore alternating current network side port, and enabling
Based on kirchhoff current and voltage law, the circuit writes positive sequence, negative sequence and zero sequence network equation Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F is equal to 0 (o) Is a non-linear circuit equation,and (3) withFor the function value of the function, and (3) withIs an unknown variable;
X 1 (o) 、X 2 (o) and X is 0 (o) Adopting typical impedance characteristic parameters of a wind power plant and a flexible-direct system as initial values, and solving a nonlinear equation set Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) ) The result of the solution is marked as X 1 (1) 、X 2 (1) And X is 0 (1) 。
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.

Claims (13)

1. The method for determining the impedance of the offshore wind power through the soft direct grid-connected system is characterized by comprising the following steps of:
acquiring voltage and current waveforms of each port of the offshore wind farm and the soft direct current converter station under steady-state working conditions and resonance working conditions;
extracting resonant frequency components of each port voltage and current waveform under a steady-state working condition and a resonant working condition, and carrying out phase sequence conversion;
constructing a port circuit network equation of the offshore wind power soft and straight sending-out system according to the resonant frequency component after the phase sequence conversion;
estimating the initial value of a circuit network equation according to harmonic components of the voltage and the current of each port under a steady-state working condition;
substituting the initial value of the equation, and iteratively solving a positive and negative zero sequence component network equation under the resonance working condition to obtain positive and negative zero sequence impedance of each wind field and the flexible straight system under the resonance frequency;
the port circuit network equation for constructing the offshore wind power soft direct delivery system comprises the following steps:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind farms to a harmonic current source i Vi And harmonic impedance z Vi In parallel, wherein subscript i is the wind farm number; equating the side ports of the offshore alternating current network of the n flexible-direct system as a harmonic voltage source u Mj And z Mj The harmonic impedance is in a series connection form, wherein the subscript j is the port number of the offshore alternating current network side of the flexible-direct system;
Aiming at the topological structure of the actual system before resonance, a circuit network equation is written according to the kirchhoff current and voltage law;
for positive sequence network Y 1 ＝F 1 (X 1 )，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity to formIs a function value, where u 1,1 (f h ),…,u m,1 (f h ) And u is equal to S1,1 (f h ),…,u Sn,1 (f h ) The positive sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th flexible-direct-system offshore alternating-current network side ports are respectively 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) The system comprises a 1 st to m seaborne wind power plant collection station network side port positive sequence harmonic current component source and a 1 st to n soft direct system seaborne alternating current network side port positive sequence harmonic current component; each positive sequence impedance component to be solvedAs an unknown variable, where z V1,1 (f h ),…,z Vm,1 (f h ) And z M1,1 (f h ),…,z Mn,1 (f h ) Equivalent positive sequence impedance of 1 st to m seaborne wind power plant collecting station network side ports and 1 st to n soft and straight system seaborne alternating current network side ports, i V1,1 (f h ),…,i Vm,1 (f h ) And u is equal to M1,1 (f h ),…,u Mn,1 (f h ) The method comprises the steps of respectively providing 1 st to m equivalent positive sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent positive sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible and straight system;
for negative sequence network Y 2 ＝F 2 (X 2 )，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity to formIs a function value, where u 1,2 (f h ),…,u m,2 (f h ) And u is equal to S1,2 (f h ),…,u Sn,2 (f h ) Respectively the 1 st to m th offshore wind farm collecting station network side ports and the 1 st to n th soft-direct system offshore alternating current network side ports negative sequence harmonic voltage components, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) The method comprises the steps of collecting a network side port negative sequence harmonic current component source of a station network of a 1 st to m-th offshore wind farm and a network side port negative sequence harmonic current component of a 1 st to n-th offshore alternating current network of a flexible and straight system respectively; each negative sequence impedance composition to be solvedAs an unknown variable, where z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Respectively equivalent negative sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,2 (f h ),…,i Vm,2 (f h ) And u is equal to M1,2 (f h ),…,u Mn,2 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent negative sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent negative sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system;
for zero sequence network Y 0 ＝F 0 (X 0 )，F 0 For nonlinear circuit equation, selecting zero sequence component composition of electric quantityIs a function value, where u 1,0 (f h ),…,u m,0 (f h ) And u is equal to S1,0 (f h ),…,u Sn,0 (f h ) The zero sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th soft-direct system offshore alternating current network side ports are respectively 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) The method comprises the steps of collecting a station network side port zero-sequence harmonic current component source of a 1 st to m th offshore wind farm and a 1 st to n th offshore alternating current network side port zero-sequence harmonic current component of a flexible direct system respectively; each zero sequence impedance component to be solvedAs an unknown variable, where z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Equivalent zero sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,0 (f h ),…,i Vm,0 (f h ) And u is equal to M1,0 (f h ),…,u Mn,0 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent zero sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent zero sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system.
2. The method for determining the impedance of the offshore wind power grid-connected system through the flexible direct connection according to claim 1, wherein the step of obtaining the voltage and current waveforms of each port of the offshore wind power plant and the flexible direct current converter station under the steady-state working condition and the resonance working condition comprises the following steps:
acquiring three-phase voltage and current waveforms of a flexible-direct system offshore alternating current network side port from intra-station wave recording;
and acquiring three-phase voltage and current waveforms of the cross current network side port of the collection station of the offshore wind farm from the wave recording in the station.
3. The method for determining the impedance of the offshore wind power via soft-direct-connected grid system according to claim 2, wherein the waveform of three-phase voltage and current of the offshore alternating-current grid side port of the soft-direct-connected grid system is represented as:
U Sa (t)＝[U S1,a (t),U S2,a (t),…,U Sn,a (t)]
U Sb (t)＝[U S1,b (t),U S2,b (t),…,U Sn,b (t)]
U Sc (t)＝[U S1,c (t),U S2,c (t),…,U Sn,c (t)]
I Sa (t)＝[I S1,a (t),I S2,a (t),…,I Sn,a (t)]
I Sb (t)＝[I S1,b (t),I S2,b (t),…,I Sn,b (t)]
I Sc (t)＝[I S1,c (t),I S2,c (t),…,I Sn,c (t)]
wherein U is Sa (t)、U Sb (t) and U Sc (t) is the voltages of a, b and c phases of the offshore alternating current network side of the flexible-direct system respectively, I Sa (t)、I Sb (t) and I Sc And (t) are the phase currents of the a, b and c sides of the offshore alternating current network of the flexible-direct system, and subscripts 1 to n respectively represent the 1 st to n th ports.
4. The method for determining the impedance of the offshore wind power through-flexible direct grid-connected system according to claim 2, wherein three-phase voltage and current waveforms of the alternating current grid side port of the offshore wind power plant collection station are expressed as follows:
U a (t)＝[U 1,a (t),U 2,a (t),…,U m,a (t)]
U b (t)＝[U 1,b (t),U 2,b (t),…,U m,b (t)]
U c (t)＝[U 1,c (t),U 2,c (t),…,U m,c (t)]
I a (t)＝[I 1,a (t),I 2,a (t),…,I m,a (t)]
I b (t)＝[I 1,b (t),I 2,b (t),…,I m,b (t)]
I c (t)＝[I 1,c (t),I 2,c (t),…,I m,c (t)]
Wherein U is a (t)、U b (t) and U c (t) is the phase voltages of a, b and c on the collecting station network side of the offshore wind farm respectively, I a (t)、I b (t) and I c And (t) are the current of the a, b and c phases of the offshore wind farm network side, and subscripts 1-m respectively represent 1-m ports.
5. The method for determining the impedance of the offshore wind power grid-connected system through flexible direct connection according to claim 4, wherein the steps of extracting the resonant frequency components of the voltage and current waveforms of each port under the steady-state working condition and the resonant working condition and performing phase sequence transformation comprise:
the voltage and current waveform pairs of different ports are paired based on the GPS time signal of the oscillograph;
selecting a time section t under a resonance working condition h At f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] h -1/(2Δf),t h +1/(2Δf)]Wherein f S The sampling frequency of the original signal is shown as delta f, and the spectrum resolution is shown as delta f; the electric quantity of the soft-direct system offshore alternating current network side port and the offshore wind farm collecting station network side port are windowed to obtain Fourier transform to obtain a soft-direct system offshore alternating current network side a, b and c phase voltage Fourier spectrum M USa (f h )、M USb (f h ) And M is as follows USc (f h ) Obtaining a Fourier spectrum M of a, b and c phase currents of the flexible-direct system offshore alternating current network side ISa (f h )、M ISb (f h ) And M is as follows ISc (f h ) Phase a, b and c voltage Fourier spectrum M of collection station network side of offshore wind farm Ua (f h )、M Ub (f h ) And M is as follows Uc (f h ) Phase a, b and c current Fourier spectrum M at collection station network side of offshore wind farm Ia (f h )、M Ib (f h ) And M is as follows Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency components of each port based on a phase sequence transformation matrix D;
the phase sequence transformation moment D is as follows:
the phase sequence transformation is as follows:
[M US1 (f h ),M US2 (f h ),M US0 (f h )] T ＝D[M USa (f h ),M USb (f h ),M USc (f h )] T
[M IS1 (f h ),M IS2 (f h ),M IS0 (f h )] T ＝D[M ISa (f h ),M ISb (f h ),M ISc (f h )] T
[M U1 (f h ),M U2 (f h ),M U0 (f h )] T ＝D[M Ua (f h ),M Ub (f h ),M Uc (f h )] T
[M I1 (f h ),M I2 (f h ),M I0 (f h )] T ＝D[M Ia (f h ),M Ib (f h ),M Ic (f h )] T
wherein M is US1 (f h )、M US2 (f h )、M US0 (f h ) The port voltage of the soft direct system offshore alternating current network side in the complex expression form is positive sequence, negative sequence and zero sequence components of the resonant frequency; m is M IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; m is M U1 (f h )、M U2 (f h )、M U0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; m is M I1 (f h )、M I2 (f h )、M I0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of station network side port current at resonant frequency for a complex expression form of the offshore wind farm;
selecting a time section t under a steady-state working condition o And t is equal to h With an interval of 1/f h Integer multiple of f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] o -1/(2Δf),t o +1/(2Δf)]Side end of offshore alternating current network of opposite-flexible-direct systemThe electric quantity of the port and the port of the collecting station network side of the offshore wind farm is windowed to obtain Fourier transform, and a, b, c phase voltage Fourier spectrum of the offshore alternating current network side of the flexible direct system is obtainedAnd->Obtaining a Fourier spectrum of a, b and c phase currents of the flexible-direct system offshore alternating current network side +. >And->Obtaining a Fourier spectrum of phase voltages of a, b and c at the collecting station network side of the offshore wind farm>And->Similarly, a Fourier spectrum of the current of phases a, b and c on the net side of the collection station of the offshore wind farm is obtained>And->
The phase sequence transformation of the electric quantity resonance frequency components of each port is as follows:
wherein,the positive sequence, negative sequence and zero sequence components of the port voltage of the offshore alternating current network side of the flexible direct current system in the complex expression form at the resonant frequency; />The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; />The current of the port of the station network side is collected for the complex expression type offshore wind farm in the positive sequence, the negative sequence and the zero sequence components of the resonant frequency.
6. The method for determining the impedance of the offshore wind power grid-connected system through flexible direct connection according to claim 1, wherein the estimating the initial value of the circuit network equation according to the harmonic component of each port voltage and each current under the steady-state working condition comprises:
for an actual system topological structure before resonance, substituting harmonic components of current of a collection station port of an offshore wind farm under normal working conditions into the actual system topological structure to serve as an equivalent harmonic current source of the collection station port of the offshore wind farm, taking harmonic components of voltage of a flexible-direct system offshore alternating current network side port under steady-state working conditions into an equivalent harmonic voltage source of the flexible-direct system offshore alternating current network side port, and enabling
Based on kirchhoff current and voltage law, the circuit writes positive sequence, negative sequence and zero sequence network equation Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F is equal to 0 (o) Is a non-linear circuit equation,and (3) withFor the function value of the function, and (3) withIs an unknown variable;
X 1 (o) 、X 2 (o) and X is 0 (o) Adopting typical impedance characteristic parameters of a wind power plant and a flexible-direct system as initial values, and solving a nonlinear equation set Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) ) The result of the solution is marked as X 1 (1) 、X 2 (1) And X is 0 (1) 。
7. The method for determining the impedance of the offshore wind power through the soft-direct-grid system according to claim 1, wherein the positive and negative zero sequence impedance process for obtaining each wind field and the soft-direct system is as follows:
for circuit network equation Y 1 ＝F 1 (X 1 )、Y 2 ＝F 2 (X 2 ) And Y is equal to 0 ＝F 0 (X 0 ) Let the initial values be respectively And (3) withIterative solving equation based on numerical method to obtain each harmonic source to be solved and positive sequence complex impedance value X 1 、X 2 And X is 0 。
8. An offshore wind power grid-connected system impedance determination system is characterized by comprising:
the voltage and current waveform acquisition module is used for acquiring voltage and current waveforms of each port of the offshore wind power plant and the flexible direct current converter station under steady-state working conditions and resonance working conditions;
the phase sequence conversion module is used for extracting resonant frequency components of each port voltage and current waveform under the steady-state working condition and the resonance working condition and carrying out phase sequence conversion;
The equation construction module is used for constructing a port circuit network equation of the offshore wind power system which is sent out from the system through flexible straight according to the resonant frequency component after the phase sequence conversion;
the operations performed by the equation construction module include:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind farms to a harmonic current source i Vi And harmonic impedance z Vi In parallel, wherein subscript i is the wind farm number; the side ports of the offshore alternating current network of n flexible and straight systems and the likeThe value is harmonic voltage source u Mj And z Mj The harmonic impedance is in a series connection form, wherein the subscript j is the port number of the offshore alternating current network side of the flexible-direct system;
aiming at the topological structure of the actual system before resonance, a circuit network equation is written according to the kirchhoff current and voltage law;
for positive sequence network Y 1 ＝F 1 (X 1 )，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity to formIs a function value, where u 1,1 (f h ),…,u m,1 (f h ) And u is equal to S1,1 (f h ),…,u Sn,1 (f h ) The positive sequence harmonic voltage components, i, of the 1 st to m-th offshore wind farm collecting station network side ports and the 1 st to n-th flexible-direct-system offshore alternating-current network side ports are respectively 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) The system comprises a 1 st to m seaborne wind power plant collection station network side port positive sequence harmonic current component source and a 1 st to n soft direct system seaborne alternating current network side port positive sequence harmonic current component; each positive sequence impedance component to be solved As an unknown variable, where z V1,1 (f h ),…,z Vm,1 (f h ) And z M1,1 (f h ),…,z Mn,1 (f h ) Equivalent positive sequence impedance of 1 st to m seaborne wind power plant collecting station network side ports and 1 st to n soft and straight system seaborne alternating current network side ports, i V1,1 (f h ),…,i Vm,1 (f h ) And u is equal to M1,1 (f h ),…,u Mn,1 (f h ) The method comprises the steps of respectively providing 1 st to m equivalent positive sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent positive sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible and straight system;
for negative sequence network Y 2 ＝F 2 (X 2 )，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity to formIs a function value, where u 1,2 (f h ),…,u m,2 (f h ) And u is equal to S1,2 (f h ),…,u Sn,2 (f h ) Respectively the 1 st to m th offshore wind farm collecting station network side ports and the 1 st to n th soft-direct system offshore alternating current network side ports negative sequence harmonic voltage components, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) The method comprises the steps of collecting a network side port negative sequence harmonic current component source of a station network of a 1 st to m-th offshore wind farm and a network side port negative sequence harmonic current component of a 1 st to n-th offshore alternating current network of a flexible and straight system respectively; each negative sequence impedance composition to be solvedAs an unknown variable, where z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Respectively equivalent negative sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,2 (f h ),…,i Vm,2 (f h ) And u is equal to M1,2 (f h ),…,u Mn,2 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent negative sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent negative sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system;
For zero sequence network Y 0 ＝F 0 (X 0 )，F 0 For nonlinear circuit equation, selecting zero sequence component composition of electric quantityIs a function value, where u 1,0 (f h ),…,u m,0 (f h ) And u is equal to S1,0 (f h ),…,u Sn,0 (f h ) Respectively 1 st to fourthZero sequence harmonic voltage components of m marine wind power plant collection station network side ports and 1 st to n th soft direct system marine alternating current network side ports, i 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) The method comprises the steps of collecting a station network side port zero-sequence harmonic current component source of a 1 st to m th offshore wind farm and a 1 st to n th offshore alternating current network side port zero-sequence harmonic current component of a flexible direct system respectively; each zero sequence impedance component to be solvedAs an unknown variable, where z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Equivalent zero sequence impedance of 1 st to m th ports of collection station of offshore wind farm and 1 st to n th ports of offshore alternating current network of flexible-direct system, i V1,0 (f h ),…,i Vm,0 (f h ) And u is equal to M1,0 (f h ),…,u Mn,0 (f h ) The method comprises the steps of respectively obtaining 1 st to m equivalent zero sequence harmonic current sources at ports of a collection station of the offshore wind farm and 1 st to n equivalent zero sequence harmonic voltage sources at ports of an offshore alternating current network of a flexible-direct system; the equation initial value calculation module is used for estimating a circuit network equation initial value according to harmonic components of the voltage and the current of each port under the steady-state working condition;
and the impedance calculation module is used for substituting the initial value of the equation, and iteratively solving the positive and negative zero sequence component network equation under the resonance working condition to obtain the positive and negative zero sequence impedance of each wind field and the flexible direct system under the resonance frequency.
9. The offshore wind power grid-tie-in system impedance determination system of claim 8, wherein the operations performed by the voltage-current waveform acquisition module comprise:
acquiring three-phase voltage and current waveforms of a flexible-direct system offshore alternating current network side port from intra-station wave recording;
and acquiring three-phase voltage and current waveforms of the cross current network side port of the collection station of the offshore wind farm from the wave recording in the station.
10. The offshore wind power grid-connected system impedance determination system according to claim 9, wherein the three-phase voltage and current waveforms of the offshore alternating current grid side port of the flexible direct system are represented as:
U Sa (t)＝[U S1,a (t),U S2,a (t),…,U Sn,a (t)]
U Sb (t)＝[U S1,b (t),U S2,b (t),…,U Sn,b (t)]
U Sc (t)＝[U S1,c (t),U S2,c (t),…,U Sn,c (t)]
I Sa (t)＝[I S1,a (t),I S2,a (t),…,I Sn,a (t)]
I Sb (t)＝[I S1,b (t),I S2,b (t),…,I Sn,b (t)]
I Sc (t)＝[I S1,c (t),I S2,c (t),…,I Sn,c (t)]
wherein U is Sa (t)、U Sb (t) and U Sc (t) is the voltages of a, b and c phases of the offshore alternating current network side of the flexible-direct system respectively, I Sa (t)、I Sb (t) and I Sc And (t) are the phase currents of the a, b and c sides of the offshore alternating current network of the flexible-direct system, and subscripts 1 to n respectively represent the 1 st to n th ports.
11. The offshore wind power grid-connected-through-soft-direct-connection system impedance determination system according to claim 10, wherein three-phase voltage and current waveforms of an alternating current grid-side port of the offshore wind farm collection station are represented as:
U a (t)＝[U 1,a (t),U 2,a (t),…,U m,a (t)]
U b (t)＝[U 1,b (t),U 2,b (t),…,U m,b (t)]
U c (t)＝[U 1,c (t),U 2,c (t),…,U m,c (t)]
I a (t)＝[I 1,a (t),I 2,a (t),…,I m,a (t)]
I b (t)＝[I 1,b (t),I 2,b (t),…,I m,b (t)]
I c (t)＝[I 1,c (t),I 2,c (t),…,I m,c (t)]
wherein U is a (t)、U b (t) and U c (t) is the phase voltages of a, b and c on the collecting station network side of the offshore wind farm respectively, I a (t)、I b (t) and I c And (t) are the current of the a, b and c phases of the offshore wind farm network side, and subscripts 1-m respectively represent 1-m ports.
12. The offshore wind power grid-tie-in system impedance determination system of claim 10, wherein the operations performed by the phase sequence transformation module comprise:
the voltage and current waveform pairs of different ports are paired based on the GPS time signal of the oscillograph;
selecting a time section t under a resonance working condition h At f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] h -1/(2Δf),t h +1/(2Δf)]Wherein f S The sampling frequency of the original signal is shown as delta f, and the spectrum resolution is shown as delta f; the electric quantity of the soft-direct system offshore alternating current network side port and the offshore wind farm collecting station network side port are windowed to obtain Fourier transform to obtain a soft-direct system offshore alternating current network side a, b and c phase voltage Fourier spectrum M USa (f h )、M USb (f h ) And M is as follows USc (f h ) Obtaining a Fourier spectrum M of a, b and c phase currents of the flexible-direct system offshore alternating current network side ISa (f h )、M ISb (f h ) And M is as follows ISc (f h ) Phase a, b and c voltage Fourier spectrum M of collection station network side of offshore wind farm Ua (f h )、M Ub (f h ) And M is as follows Uc (f h ) Phase a, b and c current Fourier spectrum M at collection station network side of offshore wind farm Ia (f h )、M Ib (f h ) And M is as follows Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency components of each port based on a phase sequence transformation matrix D;
the phase sequence transformation moment D is as follows:
The phase sequence transformation is as follows:
[M US1 (f h ),M US2 (f h ),M US0 (f h )] T ＝D[M USa (f h ),M USb (f h ),M USc (f h )] T
[M IS1 (f h ),M IS2 (f h ),M IS0 (f h )] T ＝D[M ISa (f h ),M ISb (f h ),M ISc (f h )] T
[M U1 (f h ),M U2 (f h ),M U0 (f h )] T ＝D[M Ua (f h ),M Ub (f h ),M Uc (f h )] T
[M I1 (f h ),M I2 (f h ),M I0 (f h )] T ＝D[M Ia (f h ),M Ib (f h ),M Ic (f h )] T
wherein M is US1 (f h )、M US2 (f h )、M US0 (f h ) The port voltage of the soft direct system offshore alternating current network side in the complex expression form is positive sequence, negative sequence and zero sequence components of the resonant frequency; m is M IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; m is M U1 (f h )、M U2 (f h )、M U0 (f h ) Collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; m is M I1 (f h )、M I2 (f h )、M I0 (f h ) Is complexThe current of the port of the collection station network side of the offshore wind farm in the digital expression form is positive sequence, negative sequence and zero sequence components of the resonant frequency;
selecting a time section t under a steady-state working condition o And t is equal to h With an interval of 1/f h Integer multiple of f S The/deltaf is an analysis window construction square wave signal window function g (t) =1, t= [ t ] o -1/(2Δf),t o +1/(2Δf)]The electric quantity of the port on the side of the offshore alternating current network of the flexible direct system and the electric quantity of the port on the side of the collecting station network of the offshore wind farm are windowed to obtain Fourier transform, and a phase voltage Fourier spectrum of a, b and c of the offshore alternating current network of the flexible direct system is obtainedAnd->Obtaining a Fourier spectrum of a, b and c phase currents of the flexible-direct system offshore alternating current network side +.>And->Obtaining a Fourier spectrum of phase voltages of a, b and c at the collecting station network side of the offshore wind farm>And->Similarly, a Fourier spectrum of the current of phases a, b and c on the net side of the collection station of the offshore wind farm is obtained >And->
The phase sequence transformation of the electric quantity resonance frequency components of each port is as follows:
wherein,the positive sequence, negative sequence and zero sequence components of the port voltage of the offshore alternating current network side of the flexible direct current system in the complex expression form at the resonant frequency; />The positive sequence, negative sequence and zero sequence components of the current of the port of the offshore alternating current network of the flexible direct system in the complex expression form at the resonant frequency; collecting positive sequence, negative sequence and zero sequence components of the station network side port voltage at the resonant frequency for the offshore wind farm in a complex expression form; />The current of the port of the station network side is collected for the complex expression type offshore wind farm in the positive sequence, the negative sequence and the zero sequence components of the resonant frequency.
13. The offshore wind power grid-tie-in system impedance determination system of claim 8, wherein the operation performed by the equation initial value calculation module comprises:
for an actual system topological structure before resonance, substituting harmonic components of current of a collection station port of an offshore wind farm under normal working conditions into the actual system topological structure to serve as an equivalent harmonic current source of the collection station port of the offshore wind farm, taking harmonic components of voltage of a flexible-direct system offshore alternating current network side port under steady-state working conditions into an equivalent harmonic voltage source of the flexible-direct system offshore alternating current network side port, and enabling
Based on kirchhoff current and voltage law, the circuit writes positive sequence, negative sequence and zero sequence network equation Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F is equal to 0 (o) Is a non-linear circuit equation,and (3) withFor the function value of the function, and (3) withIs an unknown variable;
X 1 (o) 、X 2 (o) and X is 0 (o) Adopting typical impedance characteristic parameters of a wind power plant and a flexible-direct system as initial values, and solving a nonlinear equation set Y 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y is equal to 0 (o) ＝F 0 (o) (X 0 (o) ) The result of the solution is marked as X 1 (1) 、X 2 (1) And X is 0 (1) 。
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