CN115313488A - Method and system for determining impedance of offshore wind power grid-connected system through flexible and direct connection - Google Patents
Method and system for determining impedance of offshore wind power grid-connected system through flexible and direct connection Download PDFInfo
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Abstract
The invention discloses an impedance determination method for an offshore wind power grid-connected system through flexible and straight connection, which comprises the following steps: acquiring voltage and current waveforms of an offshore wind farm 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 transformation; constructing a port circuit network equation of the offshore wind power transmitted out of the system through the flexible direct transmission system under the resonance frequency; calculating an initial value of a network equation of the port circuit; and (4) iteratively solving a network equation under the resonance working condition to obtain the impedance and harmonic source parameters of each wind field and the flexible-straight system. The method is based on the actually measured wave recording data, combines the window Fourier analysis and the nonlinear circuit equation solving method, realizes the rapid calculation of the impedance of the flexible-straight system and the wind power plant under the resonance working condition, greatly improves the accuracy of the broadband oscillation positioning and analysis of the offshore wind power through the flexible-straight grid-connected system compared with the existing method, and provides an analysis tool for the field debugging work of the broadband oscillation.
Description
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to an impedance determination method and system for an offshore wind power grid-connected system through flexibility and straightness.
Background
The offshore wind power is analyzed based on an offline small signal model or online impedance frequency sweeping characteristics, however, the offshore wind power plant has numerous operating conditions, a large number of power electronic devices in the flexible and straight system are complex in control strategy, and the problems of inaccuracy of an offline model and lack of an analysis tool exist in the broadband oscillation research of an actual system. The method specifically shows that a fault scene is difficult to reproduce on an offline platform after broadband oscillation occurs, and the impedance characteristics of the relevant frequency bands of the system are calculated, which brings great inconvenience to the positioning of an oscillation source and causes difficulty in further analyzing the broadband oscillation characteristics and oscillation suppression of the offshore wind power through a flexible direct grid-connected system.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an offshore wind power flexible direct grid-connected system impedance determination method, which can realize the calculation of the actual system harmonic impedance.
The technical problem to be solved by the invention is realized by the following technical scheme:
in a first aspect, an impedance determination method for offshore wind power through a flexible direct grid-connected system is provided, and is characterized by comprising the following steps:
acquiring voltage and current waveforms of ports of an offshore wind farm and a flexible direct current converter station under a steady-state working condition and a resonance working condition;
extracting resonance frequency components of voltage and current waveforms of each port under a steady state working condition and a resonance working condition and carrying out phase sequence transformation;
constructing a port circuit network equation of the offshore wind power soft and direct output system according to the resonance frequency component after the phase sequence conversion;
estimating an initial value of a circuit network equation according to harmonic components of voltage and current of each port under a steady-state working condition;
and 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 impedances of each wind field and the flexible direct system under the resonance frequency.
With reference to the first aspect, further, the obtaining voltage and current waveforms of each port of the offshore wind farm and the flexible direct current converter station under the steady state condition and the resonance condition includes:
acquiring three-phase voltage and current waveforms of a side port of an offshore alternating current network of the flexible and direct system from in-station wave recording;
and obtaining three-phase voltage and current waveforms of the side port of the AC network of the offshore wind power plant collection station by recording in a slave station.
With reference to the first aspect, further, the three-phase voltage and current waveforms at the side port of the flexible-direct-system offshore alternating-current grid are represented 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 Sa (t)、U Sb (t) and U Sc (t) the voltages of a, b and c on the offshore AC network side of the flexible-straight system, I Sa (t)、I Sb (t) and I Sc And (t) the currents of the a, b and c on the offshore alternating current network side of the flexible-straight system respectively, and subscripts 1 to n respectively represent 1 to n ports.
With reference to the first aspect, further, the three-phase voltage and current waveforms at the ac 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 a (t)、U b (t) and U c (t) the voltages of the grid sides a, b and c of the offshore wind farm collection station, I a (t)、I b (t) and I c And (t) the currents of the grid side a, the grid side b and the grid side c of the offshore wind farm collecting station are respectively shown, and subscripts 1 to m respectively represent 1 to m ports.
With reference to the first aspect, further, the extracting resonant frequency components of voltage and current waveforms of each port under the steady-state condition and the resonance condition and performing phase-sequence transformation includes:
time synchronization is carried out on voltage and current waveforms of different ports based on a recorder GPS time signal;
selecting time section t under resonance working condition h With f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf h -1/(2Δf),t h +1/(2Δf)]Wherein f is S The original signal sampling frequency is adopted, and delta f is the frequency spectrum resolution; windowing the electric quantity of the port at the side of the offshore AC network of the flexible direct system and the port at the side of the network of the offshore wind farm collection station to obtain Fourier transform of the electric quantity of the port at the side of the offshore AC network of the flexible direct system, and obtaining Fourier spectrum M of the voltages of a phase, a phase and a phase of the offshore AC network of the flexible direct system USa (f h )、M USb (f h ) And M USc (f h ) Obtaining a Fourier spectrum M of phase currents a, b and c at the side of the marine alternating current network of the flexible direct system ISa (f h )、M ISb (f h ) And M ISc (f h ) Fourier spectrum M of voltages of a, b and c at grid side of offshore wind farm collection station Ua (f h )、M Ub (f h ) And M Uc (f h ) And Fourier spectrums M of currents of a phase, b phase and c phase of offshore wind power plant network side collection stations Ia (f h )、M Ib (f h ) And M Ic (f h )；
Phase sequence transformation is carried out on the electric quantity resonance frequency component of each port based on the 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 flexible direct system offshore alternating current network side in the form of complex expression at the resonant frequency; m is a group of IS1 (f h )、M IS2 (f h )、M IS0 (f h ) Positive sequence, negative sequence and zero sequence components of the cross network side port current on the sea in the flexible-straight system in a complex expression form at the resonant frequency; (ii) a M U1 (f h )、M U2 (f h )、M U0 (f h ) Positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in a complex expression form at the resonant frequency; m I1 (f h )、M I2 (f h )、M I0 (f h ) The method comprises the steps that positive sequence, negative sequence and zero sequence components of the network side port current of the offshore wind farm collection station in a complex expression form at resonance frequency are obtained;
selecting the time section t under the steady state working condition o And t is h The interval time is 1/f h Integer multiple of f S ,/Δ f, a square-wave signal window function g (t) =1, t = [ t ] is constructed for the analysis window o -1/(2Δf),t o +1/(2Δf)]Windowing the electric quantity of the side port of the offshore AC network of the flexible direct system and the side port of the network of the offshore wind farm collection station to obtain Fourier transform of the voltage of a phase, b phase and c phase of the offshore AC network of the flexible direct system
And
obtaining phase current Fourier spectrums of a, b and c sides of an offshore alternating current network of the flexible direct current system
And
obtaining a Fourier spectrum of voltages of a, b and c phases at the grid side of the offshore wind farm collection station
And
similarly, fourier spectrums of currents of a, b and c at net side of offshore wind power plant collecting station are obtained
And with
The phase sequence conversion is carried out on the electric quantity resonance frequency component of each port as follows:
wherein the content of the first and second substances,
the positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct system offshore alternating current network side in the form of complex expression at the resonant frequency;
the method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained;
positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in a complex expression form at the resonant frequency;
the current of the network side port of the offshore wind farm collection station in the form of complex expression is the positive sequence, negative sequence and 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 output system via flexible direct output includes:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind power plants to harmonic current source i Vi And harmonic impedance z Vi A parallel connection mode, wherein a subscript i is a wind power plant number; equating the ports on the offshore alternating current network side of n flexible direct systems as harmonic voltage sources u Mj And z Mj The harmonic impedance is connected in series, wherein the subscript j is the port number of the soft and straight rectification side;
writing a circuit network equation according to kirchhoff current and voltage law sequence aiming at a real system topological structure before resonance;
y = F for positive sequence networks 1 (X)，F 1 Is a non-linear circuit equation of the type,selecting the positive sequence component of the electrical quantity
Is a function value of u in the formula 1,1 (f h ),…,u m,1 (f h ) And u S1,1 (f h ),…,u Sn,1 (f h ) Respectively are positive sequence harmonic voltage components, i, of the net side ports of the 1 st to m offshore wind farm collection station and the net side ports of the 1 st to n flexible and straight system offshore AC network 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) Respectively providing a positive sequence harmonic current component source for a network side port of a collection station of the 1 st to m offshore wind power plants and a positive sequence harmonic current component for a network side port of an offshore alternating current network of the 1 st to n flexible and straight systems; each impedance component to be determined with positive sequence
For unknown variables, in which 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, i, of the net side port of the 1 st to m offshore wind farm collection station and the offshore alternating current net side port of the 1 st to n flexible and straight system V1,1 (f h ),…,i Vm,1 (f h ) And u M1,1 (f h ),…,u Mn,1 (f h ) Respectively providing 1-m offshore wind farm collection station port equivalent positive sequence harmonic current sources and 1-n flexible direct system offshore alternating current network side port equivalent positive sequence harmonic voltage sources;
y = F for negative sequence network 2 (X)，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity
Is a function value, in which u 1,2 (f h ),…,u m,2 (f h ) And u S1,2 (f h ),…,u Sn,2 (f h ) Respectively are the network side ports of the 1 st to the m th offshore wind farm collection stations and the side ports of the 1 st to the n th flexible and straight system offshore AC networkSequence harmonic voltage component, i 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-determined negative sequence impedance component
For unknown variables, in which z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Equivalent negative sequence impedance, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n offshore alternating current network side ports of the flexible and direct systems respectively V1,2 (f h ),…,i Vm,2 (f h ) And u M1,2 (f h ),…,u Mn,2 (f h ) Respectively providing 1 st to m offshore wind farm collection station port equivalent negative sequence harmonic current sources and 1 st to n flexible direct system offshore alternating current network side port equivalent negative sequence harmonic voltage sources;
for zero sequence network Y = F 0 (X)，F 0 Selecting zero-sequence component of electric quantity to form nonlinear circuit equation
Is a function value, in which u 1,0 (f h ),…,u m,0 (f h ) And u S1,0 (f h ),…,u Sn,0 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-solved zero-sequence impedance component
For unknown variables, in which 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, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports V1,0 (f h ),…,i Vm,0 (f h ) And u M1,0 (f h ),…,u Mn,0 (f h ) The equivalent zero-sequence harmonic current sources are respectively the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports.
With reference to the first aspect, further, the estimating an initial value of the circuit network equation according to the harmonic component of the voltage and the current of each port under the steady-state condition includes:
aiming at the topological structure of an actual system before resonance, substituting the harmonic component of the offshore wind farm collection station port current under the normal working condition as an equivalent harmonic current source of the offshore wind farm collection station port, and taking the harmonic component of the offshore current network side port voltage of the flexible-direct system under the steady-state working condition as an equivalent harmonic voltage source of the offshore current network side port of the flexible-direct system to enable the harmonic component to be equivalent to the offshore current network side port of the flexible-direct system
Writing a positive sequence, a negative sequence and a zero sequence network equation Y of a circuit according to kirchhoff current and voltage law 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F 0 (o) Is a non-linear circuit equation and is,
and
is the function value of the function value,
and with
Is an unknown variable;
X 1 (o) 、X 2 (o) and X 0 (o) Solving a nonlinear equation set Y by taking a typical impedance characteristic parameter of a wind power plant and a flexible direct system as an initial value 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) ) And the solution result is marked as X 1 (1) 、X 2 (1) And X 0 (1) 。
With reference to the first aspect, further, the positive and negative zero sequence impedances of each wind field and the flexible direct current system are obtained as follows:
for circuit network equation Y 1 ＝F 1 (X 1 )、Y 2 ＝F 2 (X 2 ) And Y 0 ＝F 0 (X 0 ) Respectively give initial values of
In a second aspect, an impedance determination method for offshore wind power through a flexible direct grid-connected system is provided, and includes:
the voltage and current waveform acquisition module is used for acquiring voltage and current waveforms of ports of the offshore wind farm and the flexible direct current converter station under a steady state working condition and a resonance working condition;
the phase sequence conversion module is used for extracting resonant frequency components of voltage and current waveforms of each port under a steady-state working condition and a resonance working condition and performing phase sequence conversion;
the equation building module is used for building a port circuit network equation of the offshore wind power which is sent out of the system through the flexible and direct mode according to the resonance frequency component after the phase sequence transformation;
the equation initial value calculation module is used for estimating an equation initial value of the circuit network according to the harmonic component 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 equation initial value, 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, the voltage-current waveform obtaining module performs operations including:
acquiring three-phase voltage and current waveforms of ports on the offshore alternating current network side of the flexible direct system from the station;
and obtaining three-phase voltage and current waveforms of the side port of the AC network of the offshore wind power plant collection station by recording in a slave station.
With reference to the second aspect, further, the three-phase voltage and current waveforms of the marine ac grid side port of the flexible-straight system are represented 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 Sa (t)、U Sb (t) and U Sc (t) the voltages of the a, b and c phases of the offshore alternating current network side of the flexible-direct system I Sa (t)、I Sb (t) and I Sc And (t) the currents of the a, b and c on the offshore alternating current network side of the flexible-straight system respectively, and subscripts 1 to n respectively represent 1 to n ports.
With reference to the second aspect, further, the three-phase voltage and current waveforms at the ac 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 a (t)、U b (t) and U c (t) the voltages of the grid sides a, b and c of the offshore wind farm collection station respectively, I a (t)、I b (t) and I c And (t) the currents of the phases a, b and c on the offshore wind field network side respectively, and subscripts 1-m represent 1-m ports respectively.
With reference to the second aspect, further, the operations performed by the phase sequence transformation module include:
time synchronization is carried out on voltage and current waveforms of different ports based on a recorder GPS time signal;
selecting time section t under resonance working condition h In f with S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf h -1/(2Δf),t h +1/(2Δf)]Wherein f is S The original signal sampling frequency is adopted, and delta f is the frequency spectrum resolution; windowing the electric quantity of the port at the side of the offshore AC network of the flexible-direct system and the port at the side of the network of the offshore wind farm collection station, and performing Fourier transform to obtain a Fourier spectrum M of the voltages of a phase a, a phase b and a phase c of the offshore AC network of the flexible-direct system USa (f h )、M USb (f h ) And M USc (f h ) Obtaining a Fourier spectrum M of phase currents a, b and c at the side of the marine alternating current network of the flexible direct system ISa (f h )、M ISb (f h ) And M ISc (f h ) Fourier spectrum M of voltages of a, b and c at grid side of offshore wind farm collection station Ua (f h )、M Ub (f h ) And M Uc (f h ) And Fourier spectrums M of currents a, b and c at net sides of offshore wind farm collection station Ia (f h )、M Ib (f h ) And M Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency component of each port based on the 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 flexible direct offshore alternating current network side system in a complex expression form has positive sequence, negative sequence and zero sequence components at the resonant frequency; m IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained; m U1 (f h )、M U2 (f h )、M U0 (f h ) The positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in the form of complex expression at the resonant frequency; m I1 (f h )、M I2 (f h )、M I0 (f h ) The method comprises the steps that positive sequence, negative sequence and zero sequence components of network side port currents of an offshore wind farm collection station in a complex expression form at resonance frequency are obtained;
selecting time section t under steady state working condition o And t is h The interval time is 1/f h Integer multiple of f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf o -1/(2Δf),t o +1/(2Δf)]Windowing the electric quantity of the side port of the offshore AC network of the flexible direct system and the side port of the network of the offshore wind farm collection station to obtain Fourier transform of the voltage of a phase, b phase and c phase of the offshore AC network of the flexible direct system
And with
Obtaining phase current Fourier spectrums of a, b and c sides of an offshore alternating current network of the flexible direct current system
And
and obtaining a Fourier spectrum of voltages of a, b and c phases at the grid side of the offshore wind power plant collection station
And
similarly, fourier spectrums of currents of a, b and c at net side of offshore wind power plant collecting station are obtained
And with
The phase sequence conversion is carried out on the electric quantity resonance frequency component of each port as follows:
wherein, the first and the second end of the pipe are connected with each other,
in the form of a plural expressionThe positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct system offshore alternating current network side at the resonant frequency;
positive sequence, negative sequence and zero sequence components of the cross network side port current on the sea in the flexible-straight system in a complex expression form at the resonant frequency;
the positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in the form of complex expression at the resonant frequency;
the system comprises positive sequence, negative sequence and zero sequence components of the network side port current of the offshore wind farm collection station in a complex expression form at the resonant frequency.
With reference to the second aspect, further, the equation building module performs operations including:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind power plants to harmonic current source i Vi And harmonic impedance z Vi A parallel connection mode, wherein a subscript i is a wind power plant number; equating the ports on the offshore alternating current network side of n flexible direct systems as harmonic voltage sources u Mj And z Mj The harmonic impedance is connected in series, wherein a subscript j is the serial number of ports on the offshore alternating current network side of the flexible-straight system;
writing a circuit network equation according to kirchhoff current and voltage law sequence aiming at a real system topological structure before resonance;
y = F for positive sequence networks 1 (X)，F 1 Selecting positive sequence component of electric quantity for nonlinear circuit equation
Is a function value, in which u 1,1 (f h ),…,u m,1 (f h ) And u S1,1 (f h ),…,u Sn,1 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each impedance component to be determined in positive sequence
For unknown variables, in which 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, i, of the net side port of the 1 st to m offshore wind farm collection station and the offshore alternating current net side port of the 1 st to n flexible and straight system V1,1 (f h ),…,i Vm,1 (f h ) And u M1,1 (f h ),…,u Mn,1 (f h ) Respectively providing 1-m offshore wind farm collection station port equivalent positive sequence harmonic current sources and 1-n flexible direct system offshore alternating current network side port equivalent positive sequence harmonic voltage sources;
y = F for negative sequence networks 2 (X)，F 2 Selecting negative sequence component of electric quantity to form nonlinear circuit equation
Is a function value, in which u 1,2 (f h ),…,u m,2 (f h ) And u S1,2 (f h ),…,u Sn,2 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) Respectively being a 1 st to m offshore wind farm collection station network side port positive sequence harmonic current component source and a 1 st to cPositive sequence harmonic current components of side ports of the marine alternating current network of the n flexible direct systems; each to-be-determined negative sequence impedance component
For unknown variables, in which z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Equivalent negative sequence impedance, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible and direct system offshore alternating current network side ports V1,2 (f h ),…,i Vm,2 (f h ) And u M1,2 (f h ),…,u Mn,2 (f h ) Respectively providing 1 st to m offshore wind farm collection station port equivalent negative sequence harmonic current sources and 1 st to n flexible direct system offshore alternating current network side port equivalent negative sequence harmonic voltage sources;
y = F for zero sequence network 0 (X)，F 0 Selecting zero-sequence component composition of electric quantity for nonlinear circuit equation
Is a function value of u in the formula 1,0 (f h ),…,u m,0 (f h ) And u S1,0 (f h ),…,u Sn,0 (f h ) Respectively are positive sequence harmonic voltage components, i, of the net side ports of the 1 st to m offshore wind farm collection station and the net side ports of the 1 st to n flexible and straight system offshore AC network 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) Respectively providing a positive sequence harmonic current component source for a network side port of a collection station of the 1 st to m offshore wind power plants and a positive sequence harmonic current component for a network side port of an offshore alternating current network of the 1 st to n flexible and straight systems; each to-be-solved zero sequence impedance component
For unknown variables, in which z V1,0 (f h ),…,z Vm,0 (f h ) And z M1,0 (f h ),…,z Mn,0 (f h ) Respectively are 1 st to m offshore wind farm collection station ports andequivalent zero sequence impedance i of side ports of 1-n flexible direct system offshore alternating current network V1,0 (f h ),…,i Vm,0 (f h ) And u M1,0 (f h ),…,u Mn,0 (f h ) The equivalent zero-sequence harmonic current sources are respectively the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports.
With reference to the second aspect, further, the equation initial value calculation module performs operations including:
aiming at the topological structure of an actual system before resonance, substituting the harmonic component of the offshore wind farm collection station port current under the normal working condition as an equivalent harmonic current source of the offshore wind farm collection station port, and taking the harmonic component of the offshore current network side port voltage of the flexible-direct system under the steady-state working condition as an equivalent harmonic voltage source of the offshore current network side port of the flexible-direct system to enable the harmonic component to be equivalent to the offshore current network side port of the flexible-direct system
Writing a positive sequence, a negative sequence and a zero sequence network equation Y of a circuit according to kirchhoff current and voltage law 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F 0 (o) Is a non-linear circuit equation and is,
and
is the function value of the function value,
and with
Is an unknown variable;
X 1 (o) 、X 2 (o) and X 0 (o) Solving a nonlinear equation set Y by taking a typical impedance characteristic parameter of the wind power plant and the flexible direct system as an initial value 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) ) And the solution result is marked as X 1 (1) 、X 2 (1) And X 0 (1) 。
Has the advantages that: the method comprises the steps of writing an electric network equation according to measured electric quantities under harmonic frequency of each port 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 flexible direct grid-connected system; and reasonably setting initial values of equivalent impedance of the offshore wind power plant and the flexible direct system to iteratively solve the equation, and realizing calculation and analysis of the harmonic impedance characteristic of the actual system.
Drawings
FIG. 1 is a flow chart of the method for determining the impedance of the offshore wind power system through the flexible-direct grid-connected system.
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 an impedance determination method for offshore wind power through a flexible direct grid-connected system,
acquiring voltage and current waveforms of ports of an offshore wind farm to be analyzed and a flexible direct current converter station under a steady-state working condition and a resonance working condition.
For offshore wind power containing m wind power plants and n flexible and direct rectification ports, acquiring three-phase voltage and current waveforms of the side ports of an offshore alternating current network of the flexible and direct system through a flexible and direct grid-connected system and recording the three-phase voltage and current waveforms 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 Sa (t)、U Sb (t) and U Sc (t) the voltages of a, b and c on the offshore AC network side of the flexible-straight system, I Sa (t)、I Sb (t) and I Sc And (t) the currents of the a, b and c on the offshore alternating current network side of the flexible-straight system respectively, and subscripts 1 to n respectively represent 1 to n ports.
Obtaining three-phase voltage and current waveforms of an alternating current network side port of an offshore wind farm collection station by recording waves in a slave station, and recording 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 a (t)、U b (t) and U c (t) the voltages of a, b and c on the offshore wind field grid side respectively, I a (t)、I b (t) and I c And (t) the currents of the network side a, the network side b and the network side c of the offshore wind farm are respectively shown, and subscripts 1 to m respectively represent 1 to m ports.
And step two, preprocessing port voltage and current waveforms under different working conditions (steady state working conditions and resonance working conditions), extracting resonance frequency components and carrying out phase sequence transformation. The method specifically comprises the following steps:
s1, time synchronization is carried out on voltage and current waveforms of different ports based on a GPS time signal of a wave recorder;
s2, selecting a time section t under a resonance working condition h With f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf h -1/(2Δf),t h +1/(2Δf)]Wherein f is S For the original signal sampling frequency, Δ f is the spectral resolution. Windowing the electric quantity of the port at the side of the offshore AC network of the flexible-direct system and the port at the side of the network of the offshore wind farm collection station to obtain Fourier spectrums of the voltages of the a phase, the b phase and the c phase of the offshore AC network of the flexible-direct system
And
obtaining phase current Fourier spectrums of a, b and c sides of an offshore alternating current network of the flexible direct current system
And
and Fourier spectrums of voltages of a phase, b phase and c phase on the grid side of the offshore wind farm collection station
And with
Obtaining Fourier spectrums of currents a, b and c at net sides of offshore wind farm collection station
And with
Subscripts 1 to n represent 1 to n-th ports, respectively; similarly, fourier spectrums M of currents a, b and c at the wind field network side can be obtained Ia (f h )、M Ib (f h ) And M Ic (f h ) Subscripts 1 to m represent 1 to m ports, respectively.
S3, performing phase sequence transformation on the electric quantity resonance frequency component of each port based on the phase sequence transformation moment D
The phase sequence transformation moment D is shown below
The method comprises the following specific 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 the content of the first and second substances,
positive sequence, negative sequence and zero sequence components of voltage and current of each port on the marine alternating current network side of the flexible direct current system in a complex expression form at resonance frequency respectively;
the positive sequence, negative sequence and zero sequence components of the voltage and current of each port on the network side of the offshore wind farm collection station in the form of complex expression are respectively at the resonant frequency.
S4, selecting a time section t under a steady state working condition o And t is h The interval time is 1/f h Integer multiple of f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf o -1/(2Δf),t o +1/(2Δf)]Windowing the electric quantity of the side port of the offshore AC network of the flexible-direct system and the side port of the network of the offshore wind farm collection station to obtain Fourier transform of the electric quantity of the side port of the offshore AC network of the flexible-direct system, and obtaining Fourier spectrums of the currents of the a, b and c phases of the offshore AC network of the flexible-direct system
And with
Obtaining Fourier spectrums of phase currents a, b and c at sea alternating current network side of flexible and direct system
And
obtaining a Fourier spectrum of voltages of a, b and c phases at the grid side of the offshore wind farm collection station
And
subscripts 1 to n represent 1 to n ports, respectively; similarly, fourier spectrums of currents of a, b and c at net side of offshore wind power plant collecting station are obtained
And
subscripts 1 to m represent 1 to m ports, respectively.
The phase sequence conversion is carried out on the electric quantity resonance frequency component of each port as follows:
wherein, the first and the second end of the pipe are connected with each other,
positive sequence, negative sequence and zero sequence components of voltage and current of each port on the marine alternating current network side of the flexible direct current system in a complex expression form at resonant frequency；
And step three, constructing a port circuit network equation of the offshore wind power soft and direct sending system.
Aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind power plants to harmonic current source i Vi And harmonic impedance z Vi A parallel connection mode, wherein a subscript i is a wind power plant number; equating the side ports of the offshore alternating current network of the n flexible direct systems as harmonic voltage sources u Mj And z Mj The harmonic impedance is in series connection, wherein the subscript j is the flexible direct system offshore alternating current network side port number.
Aiming at the actual system topological structure before resonance, a circuit network equation is written according to kirchhoff current and voltage law.
Y = F for positive sequence networks 1 (X)，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity
Is a function value, in which u 1,1 (f h ),…,u m,1 (f h ) And u S1,1 (f h ),…,u Sn,1 (f h ) Respectively are positive sequence harmonic voltage components, i, of the net side ports of the 1 st to m offshore wind farm collection station and the net side ports of the 1 st to n flexible and straight system offshore AC network 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) Respectively providing a positive sequence harmonic current component source for a network side port of a collection station of the 1 st to m offshore wind power plants and a positive sequence harmonic current component for a network side port of an offshore alternating current network of the 1 st to n flexible and straight systems; each impedance component to be determined in positive sequence
For unknown variables, in which 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, i, of the 1 st to m th offshore wind farm ports and the 1 st to n th flexible and direct system offshore alternating current network side ports on the collection station network side V1,1 (f h ),…,i Vm,1 (f h ) And u M1,1 (f h ),…,u Mn,1 (f h ) The equivalent positive sequence harmonic current sources are respectively the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports.
Y = F for negative sequence network 2 (X)，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity
Is a function value of u in the formula 1,2 (f h ),…,u m,2 (f h ) And u S1,2 (f h ),…,u Sn,2 (f h ) Respectively are positive sequence harmonic voltage components, i, of the net side ports of the 1 st to m offshore wind farm collection station and the net side ports of the 1 st to n flexible and straight system offshore AC network 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-determined negative sequence impedance component
For unknown variables, in which z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Equivalent negative sequence impedance, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible and direct system offshore alternating current network side ports V1,2 (f h ),…,i Vm,2 (f h ) And u M1,2 (f h ),…,u Mn,2 (f h ) Are respectively 1 st to m thThe equivalent negative sequence harmonic current source at the port of the offshore wind power plant collection station and the equivalent negative sequence harmonic voltage source at the side port of the offshore alternating current network of the 1 st to nth flexible direct systems.
For zero sequence network Y = F 0 (X)，F 0 Selecting zero-sequence component composition of electric quantity for nonlinear circuit equation
Is a function value of u in the formula 1,0 (f h ),…,u m,0 (f h ) And u S1,0 (f h ),…,u Sn,0 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) Respectively providing a positive sequence harmonic current component source for a network side port of a collection station of the 1 st to m offshore wind power plants and a positive sequence harmonic current component for a network side port of an offshore alternating current network of the 1 st to n flexible and straight systems; each to-be-solved zero sequence impedance component
For unknown variables, in which 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, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports V1,0 (f h ),…,i Vm,0 (f h ) And u M1,0 (f h ),…,u Mn,0 (f h ) The equivalent zero-sequence harmonic current sources of the ports of the collecting station of the 1 st to m offshore wind power plants and the equivalent zero-sequence harmonic voltage sources of the ports of the offshore alternating current networks of the 1 st to n flexible direct systems are respectively arranged.
Step four, calculating the initial value of the network equation of the port circuit based on the harmonic component of the voltage and the current of each port under the normal working condition, wherein the step comprises the following steps:
s1, aiming at a topological structure of an actual system before resonance, substituting a harmonic component of current at a port of an offshore wind farm collection station under a normal working condition to be used as an equivalent harmonic current source of the port of the offshore wind farm collection station, and using a harmonic component of voltage at an end port of an offshore current network of a flexible-direct system under a steady working condition as an equivalent harmonic voltage source of the end port of the offshore current network of the flexible-direct system, so that
Writing a positive sequence, a negative sequence and a zero sequence network equation Y of a circuit according to kirchhoff current and voltage law 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F 0 (o) Is a non-linear circuit equation of the type,
and
is the function value of the function value,
and
is an unknown variable.
S2，X 1 (o) 、X 2 (o) And X 0 (o) The method is characterized in that a wind power plant and a flexible direct system typical impedance characteristic parameter are used as initial values, and a nonlinear equation set Y is solved 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 0 (o) ＝F 0 (o) (X 0 (o) ) And the solution result is marked as X 1 (1) 、X 2 (1) And X 0 (1) 。
And step five, substituting the equation initial value, and iteratively solving a positive and negative zero-sequence component network equation under the resonance working condition to obtain positive and negative zero-sequence impedances 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 0 ＝F 0 (X 0 ) Respectively give an initial value of
Example 2
The invention also provides an offshore wind power flexible-direct grid-connected system impedance determination system, which comprises:
the voltage and current waveform acquisition module is used for acquiring voltage and current waveforms of ports of the offshore wind farm and the flexible direct current converter station under a steady state working condition and a resonance working condition;
the phase sequence conversion module is used for extracting resonant frequency components of voltage and current waveforms of each port under a steady state working condition and a resonance working condition and carrying out phase sequence conversion;
the equation building module is used for building a port circuit network equation of the offshore wind power which is sent out of the system through the flexible and direct mode according to the resonance frequency component after the phase sequence transformation;
the equation initial value calculation module is used for estimating an equation initial value of the circuit network according to harmonic components of voltage and current of each port under a steady-state working condition;
and the impedance calculation module is used for substituting the equation initial value, 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.
Wherein the voltage-current waveform obtaining module performs operations including:
acquiring three-phase voltage and current waveforms of a side port of an offshore alternating current network of the flexible and direct system from in-station wave recording;
and obtaining three-phase voltage and current waveforms of the side port of the AC network of the offshore wind power plant collection station by recording in a slave station.
The phase sequence transformation module performs operations comprising:
time synchronization is carried out on voltage and current waveforms of different ports based on a recorder GPS time signal;
selecting time section t under resonance working condition h With f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf h -1/(2Δf),t h +1/(2Δf)]Wherein f is S The original signal sampling frequency is adopted, and delta f is the frequency spectrum resolution; windowing the electric quantity of the port at the side of the offshore AC network of the flexible direct system and the port at the side of the network of the offshore wind farm collection station to obtain Fourier transform of the electric quantity of the port at the side of the offshore AC network of the flexible direct system, and obtaining Fourier spectrum M of the voltages of a phase, a phase and a phase of the offshore AC network of the flexible direct system USa (f h )、M USb (f h ) And M USc (f h ) Obtaining phase current Fourier spectrums M of a, b and c at the offshore alternating current network side of the flexible-direct system ISa (f h )、M ISb (f h ) And M ISc (f h ) Fourier spectrum M of voltages of a, b and c at grid side of offshore wind farm collection station Ua (f h )、M Ub (f h ) And M Uc (f h ) And the Fourier spectra M of the currents of a, b and c at the net side of the offshore wind farm collecting station Ia (f h )、M Ib (f h ) And M Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency component of each port based on the 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 US1 (f h )、M US2 (f h )、M US0 (f h ) Positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct offshore alternating current network side system in a complex expression form at the resonant frequency; m is a group of IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained; m U1 (f h )、M U2 (f h )、M U0 (f h ) Sea in complex expression formPositive sequence, negative sequence and zero sequence components of the voltage of the network side port of the upper wind power plant collection station at the resonant frequency; m is a group of I1 (f h )、M I2 (f h )、M I0 (f h ) The method comprises the steps that positive sequence, negative sequence and zero sequence components of network side port currents of an offshore wind farm collection station in a complex expression form at resonance frequency are obtained;
selecting time section t under steady state working condition o And t is h The interval time is 1/f h Integer multiple of f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf o -1/(2Δf),t o +1/(2Δf)]Windowing the electric quantity of the side port of the offshore AC network of the flexible direct system and the side port of the network of the offshore wind farm collection station to obtain Fourier transform of the voltage of a phase, b phase and c phase of the offshore AC network of the flexible direct system
And with
Obtaining phase current Fourier spectrums of a, b and c sides of an offshore alternating current network of the flexible direct current system
And
and obtaining a Fourier spectrum of voltages of a, b and c phases at the grid side of the offshore wind power plant collection station
And
similarly, fourier spectrums of currents of a, b and c at net side of offshore wind power plant collecting station are obtained
And with
The phase sequence conversion is carried out on the electric quantity resonance frequency component of each port as follows:
wherein the content of the first and second substances,
the positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct system offshore alternating current network side in the form of complex expression at the resonant frequency;
the method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained;
the positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in the form of complex expression at the resonant frequency;
the system comprises positive sequence, negative sequence and zero sequence components of the network side port current of the offshore wind farm collection station in a complex expression form at the resonant frequency.
The equation building block performs operations including:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; wind power mCurrent source i with harmonic value of field Vi And harmonic impedance z Vi A parallel connection mode, wherein a subscript i is a wind power plant number; equating the ports on the offshore alternating current network side of n flexible direct systems as harmonic voltage sources u Mj And z Mj The harmonic impedance is connected in series, wherein a subscript j is the serial number of ports on the offshore alternating current network side of the flexible-straight system;
writing a circuit network equation according to kirchhoff current and voltage law aiming at a topological structure of an actual system before resonance;
y = F for positive sequence networks 1 (X)，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity
Is a function value of u in the formula 1,1 (f h ),…,u m,1 (f h ) And u S1,1 (f h ),…,u Sn,1 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each impedance component to be determined in positive sequence
For unknown variables, in which 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, i, of the net side port of the 1 st to m offshore wind farm collection station and the offshore alternating current net side port of the 1 st to n flexible and straight system V1,1 (f h ),…,i Vm,1 (f h ) And u M1,1 (f h ),…,u Mn,1 (f h ) Respectively being equivalent positive sequence harmonic current sources of 1 st to m offshore wind farm collection station ports and equivalent positive sequence harmonic current sources of 1 st to n flexible direct system offshore alternating current network side portsA sequence harmonic voltage source;
y = F for negative sequence network 2 (X)，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity
Is a function value of u in the formula 1,2 (f h ),…,u m,2 (f h ) And u S1,2 (f h ),…,u Sn,2 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) Respectively providing a positive sequence harmonic current component source for a network side port of a collection station of the 1 st to m offshore wind power plants and a positive sequence harmonic current component for a network side port of an offshore alternating current network of the 1 st to n flexible and straight systems; each to-be-determined negative sequence impedance component
For unknown variables, in which z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Equivalent negative sequence impedance, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible and direct system offshore alternating current network side ports V1,2 (f h ),…,i Vm,2 (f h ) And u M1,2 (f h ),…,u Mn,2 (f h ) Respectively providing 1 st to m offshore wind farm collection station port equivalent negative sequence harmonic current sources and 1 st to n flexible direct system offshore alternating current network side port equivalent negative sequence harmonic voltage sources;
y = F for zero sequence network 0 (X)，F 0 Selecting zero-sequence component composition of electric quantity for nonlinear circuit equation
Is a function value of u in the formula 1,0 (f h ),…,u m,0 (f h ) And u S1,0 (f h ),…,u Sn,0 (f h ) Respectively are positive sequence harmonic voltage components, i, of the net side ports of the 1 st to m offshore wind farm collection station and the net side ports of the 1 st to n flexible and straight system offshore AC network 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-solved zero-sequence impedance component
For unknown variables, in which 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, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports V1,0 (f h ),…,i Vm,0 (f h ) And u M1,0 (f h ),…,u Mn,0 (f h ) The equivalent zero-sequence harmonic current sources are respectively the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports.
The equation initial value calculation module executes the operations of:
aiming at the topological structure of an actual system before resonance, substituting the harmonic component of the offshore wind farm collection station port current under the normal working condition as an equivalent harmonic current source of the offshore wind farm collection station port, and taking the harmonic component of the offshore current network side port voltage of the flexible-direct system under the steady-state working condition as an equivalent harmonic voltage source of the offshore current network side port of the flexible-direct system to enable the harmonic component to be equivalent to the offshore current network side port of the flexible-direct system
According to kirchhoff's law of current and voltageNetwork equation Y of positive sequence, negative sequence and zero sequence of column writing circuit 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F 0 (o) Is a non-linear circuit equation and is,
and with
Is a function value, and is a function value,
and with
Is an unknown variable;
X 1 (o) 、X 2 (o) and X 0 (o) Solving a nonlinear equation set Y by taking a typical impedance characteristic parameter of the wind power plant and the flexible direct system as an initial value 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) ) And the solution result is marked as X 1 (1) 、X 2 (1) And X 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 flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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 solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (15)
1. An impedance determination method for offshore wind power through a flexible-straight grid-connected system is characterized by comprising the following steps:
acquiring voltage and current waveforms of ports of an offshore wind farm and a flexible direct current converter station under a steady-state working condition and a resonance working condition;
extracting resonance frequency components of voltage and current waveforms of each port under a steady state working condition and a resonance working condition and carrying out phase sequence transformation;
constructing a port circuit network equation of the offshore wind power soft and direct output system according to the resonance frequency component after the phase sequence conversion;
estimating an initial value of a circuit network equation according to harmonic components of voltage and 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 impedances of each wind field and the flexible direct system under the resonance frequency.
2. The method for determining the impedance of the offshore wind power grid-connected system through the flexible direct current according to claim 1, wherein the step of acquiring 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 side port of an offshore alternating current network of the flexible and direct system from in-station wave recording;
and obtaining three-phase voltage and current waveforms of the side port of the AC network of the offshore wind power plant collection station by recording in a slave station.
3. The method for determining the impedance of the offshore wind power grid-connected flexible and direct system according to claim 2, wherein the three-phase voltage and current waveform of the offshore alternating current grid side port of the flexible and direct system is represented 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 Sa (t)、U Sb (t) and U Sc (t) the voltages of a, b and c on the offshore AC network side of the flexible-straight system, I Sa (t)、I Sb (t) and I Sc And (t) the currents of the a, b and c on the offshore alternating current network side of the flexible-straight system respectively, and subscripts 1 to n respectively represent 1 to n ports.
4. The method for determining the impedance of the offshore wind power grid-connected flexible-direct system according to claim 2, wherein the three-phase voltage and current waveform of the AC grid side port of the offshore wind farm collection station is represented 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 a (t)、U b (t) and U c (t) the voltages of the grid sides a, b and c of the offshore wind farm collection station, I a (t)、I b (t) and I c And (t) the currents of the phases a, b and c on the offshore wind field network side respectively, and subscripts 1-m represent 1-m ports respectively.
5. The method for determining the impedance of the offshore wind power grid-connected system through flexibility and straightness as claimed in claim 4, wherein the step of extracting the resonant frequency components of the voltage and current waveforms of each port under the steady state condition and the resonance condition and performing the phase sequence transformation comprises the steps of:
time synchronization is carried out on voltage and current waveforms of different ports based on a recorder GPS time signal;
selecting time section t under resonance working condition h With f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf h -1/(2Δf),t h +1/(2Δf)]Wherein f is S The original signal sampling frequency is adopted, and delta f is the frequency spectrum resolution; windowing the electric quantity of the port at the side of the offshore AC network of the flexible direct system and the port at the side of the network of the offshore wind farm collection station to obtain Fourier transform of the electric quantity of the port at the side of the offshore AC network of the flexible direct system, and obtaining Fourier spectrum M of the voltages of a phase, a phase and a phase of the offshore AC network of the flexible direct system USa (f h )、M USb (f h ) And M USc (f h ) Obtaining phase current Fourier spectrums M of a, b and c at the offshore alternating current network side of the flexible-direct system ISa (f h )、M ISb (f h ) And M ISc (f h ) Fourier spectrum M of voltages of a, b and c at grid side of offshore wind farm collection station Ua (f h )、M Ub (f h ) And M Uc (f h ) And Fourier spectrums M of currents a, b and c at net sides of offshore wind farm collection station Ia (f h )、M Ib (f h ) And M Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency component of each port based on the 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 US1 (f h )、M US2 (f h )、M US0 (f h ) The port voltage of the flexible direct offshore alternating current network side system in a complex expression form has positive sequence, negative sequence and zero sequence components at the resonant frequency; m is a group of IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained; m U1 (f h )、M U2 (f h )、M U0 (f h ) The positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in the form of complex expression at the resonant frequency; m I1 (f h )、M I2 (f h )、M I0 (f h ) The method comprises the steps that positive sequence, negative sequence and zero sequence components of the network side port current of the offshore wind farm collection station in a complex expression form at resonance frequency are obtained;
selecting time section t under steady state working condition o And t is h The interval time is 1/f h Integral multiple of, in f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf o -1/(2Δf),t o +1/(2Δf)]Windowing the electric quantity of an offshore AC network side port of the flexible-direct system and an offshore wind farm collection station network side port to obtain Fourier transform, and obtaining a phase voltage Fourier spectrum of a, b and c phase voltages of the offshore AC network side of the flexible-direct system
And
obtaining phase current Fourier spectrums of a, b and c sides of an offshore alternating current network of the flexible direct current system
And
and obtaining a Fourier spectrum of voltages of a, b and c phases at the grid side of the offshore wind power plant collection station
And
similarly, fourier spectrums of currents of a, b and c at net side of offshore wind power plant collecting station are obtained
And
the phase sequence transformation is carried out on the electric quantity resonance frequency component of each port as follows:
wherein, the first and the second end of the pipe are connected with each other,
the positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct system offshore alternating current network side in the form of complex expression at the resonant frequency;
the method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained;
the positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in the form of complex expression at the resonant frequency;
the current of the network side port of the offshore wind farm collection station in the form of complex expression is the positive sequence, negative sequence and zero sequence components of the resonant frequency.
6. The method for determining the impedance of the offshore wind power system through flexible direct grid connection system according to claim 4, wherein the step of constructing a port circuit network equation of the offshore wind power system through flexible direct grid connection 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 power plants to harmonic current source i Vi And harmonic impedance z Vi A parallel connection mode, wherein a subscript i is a wind power plant number; equating the side ports of the offshore alternating current network of the n flexible direct systems as harmonic voltage sources u Mj And z Mj The harmonic impedance is connected in series, wherein a subscript j is the serial number of ports on the offshore alternating current network side of the flexible-direct system;
writing a circuit network equation according to kirchhoff current and voltage law aiming at a topological structure of an actual system before resonance;
y = F for positive sequence networks 1 (X)，F 1 For non-linear circuit equations, selecting electricityPositive sequence component composition of gas
Is a function value of u in the formula 1,1 (f h ),…,u m,1 (f h ) And u S1,1 (f h ),…,u Sn,1 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each impedance component to be determined with positive sequence
For unknown variables, in which 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, i, of the net side port of the 1 st to m offshore wind farm collection station and the offshore alternating current net side port of the 1 st to n flexible and straight system V1,1 (f h ),…,i Vm,1 (f h ) And u M1,1 (f h ),…,u Mn,1 (f h ) Equivalent positive sequence harmonic current sources of ports of collecting stations of 1 st to m offshore wind power plants and equivalent positive sequence harmonic voltage sources of ports of offshore alternating current networks of 1 st to n flexible direct systems are respectively arranged;
y = F for negative sequence network 2 (X)，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity
Is a function value of u in the formula 1,2 (f h ),…,u m,2 (f h ) And u S1,2 (f h ),…,u Sn,2 (f h ) Respectively being the net side ports of the 1 st to m offshore wind farm collection station and the 1 st to n flexible and straight system seasPositive sequence harmonic voltage component, i, at the port of the upper network side 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-determined negative sequence impedance component
For unknown variables, in which z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Equivalent negative sequence impedance, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible and direct system offshore alternating current network side ports V1,2 (f h ),…,i Vm,2 (f h ) And u M1,2 (f h ),…,u Mn,2 (f h ) Respectively providing 1 st to m offshore wind farm collection station port equivalent negative sequence harmonic current sources and 1 st to n flexible direct system offshore alternating current network side port equivalent negative sequence harmonic voltage sources;
y = F for zero sequence network 0 (X)，F 0 Selecting zero-sequence component of electric quantity to form nonlinear circuit equation
Is a function value of u in the formula 1,0 (f h ),…,u m,0 (f h ) And u S1,0 (f h ),…,u Sn,0 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-solved zero sequence impedance component
For unknown variables, in which 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, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports V1,0 (f h ),…,i Vm,0 (f h ) And u M1,0 (f h ),…,u Mn,0 (f h ) The equivalent zero-sequence harmonic current sources are respectively the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports.
7. The method for determining the impedance of the offshore wind power grid-connected system through flexibility and straightness as claimed in claim 6, wherein the estimating the initial value of the circuit network equation according to the harmonic component of the voltage and the current of each port under the steady state working condition comprises:
aiming at the topological structure of an actual system before resonance, substituting the harmonic component of the offshore wind farm collection station port current under the normal working condition as an equivalent harmonic current source of the offshore wind farm collection station port, and taking the harmonic component of the offshore current network side port voltage of the flexible-direct system under the steady-state working condition as an equivalent harmonic voltage source of the offshore current network side port of the flexible-direct system to enable the harmonic component to be equivalent to the offshore current network side port of the flexible-direct system
Writing a network equation Y of positive sequence, negative sequence and zero sequence of a circuit according to a kirchhoff current and voltage law 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F 0 (o) Is a non-linear circuit equation of the type,
and with
Is a function value, and is a function value,
and with
Is an unknown variable;
X 1 (o) 、X 2 (o) and X 0 (o) Solving a nonlinear equation set Y by taking a typical impedance characteristic parameter of the wind power plant and the flexible direct system as an initial value 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) ) And the solution result is marked as X 1 (1) 、X 2 (1) And X 0 (1) 。
8. The method for determining the impedance of the offshore wind power grid-connected flexible and straight system according to claim 6, wherein the positive and negative zero sequence impedances of each wind field and the flexible and straight system are obtained as follows:
for circuit network equation Y 1 ＝F 1 (X 1 )、Y 2 ＝F 2 (X 2 ) And Y 0 ＝F 0 (X 0 ) Respectively give an initial value of
9. An offshore wind power impedance determination system through a flexible direct grid-connected system, comprising:
the voltage and current waveform acquisition module is used for acquiring voltage and current waveforms of ports of the offshore wind farm and the flexible direct current converter station under a steady state working condition and a resonance working condition;
the phase sequence conversion module is used for extracting resonant frequency components of voltage and current waveforms of each port under a steady-state working condition and a resonance working condition and performing phase sequence conversion;
the equation building module is used for building a port circuit network equation of the offshore wind power transmitted out of the system through the flexible direct transmission according to the resonance frequency component after the phase sequence conversion;
the equation initial value calculation module is used for estimating an equation initial value of the circuit network according to harmonic components of voltage and current of each port under a steady-state working condition;
and the impedance calculation module is used for substituting the equation initial value, 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.
10. The offshore wind power through-grid-flexible system impedance determination system according to claim 9, wherein the voltage-current waveform acquisition module performs operations comprising:
acquiring three-phase voltage and current waveforms of a side port of an offshore alternating current network of the flexible and direct system from in-station wave recording;
and obtaining three-phase voltage and current waveforms of the side port of the AC network of the offshore wind power plant collection station by recording in a slave station.
11. The offshore wind power grid-connected flexible system impedance determination system according to claim 10, wherein the flexible system offshore alternating current grid side port three-phase voltage and current waveform 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 Sa (t)、U Sb (t) and U Sc (t) the voltages of the a, b and c phases of the offshore alternating current network side of the flexible-direct system I Sa (t)、I Sb (t) and I Sc And (t) the currents of the a, b and c on the offshore alternating current network side of the flexible-straight system respectively, and subscripts 1 to n respectively represent 1 to n ports.
12. The offshore wind power grid-tied flexible system impedance determination system according to claim 10, wherein the offshore wind farm collection station ac grid side port three-phase voltage and current waveforms 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 a (t)、U b (t) and U c (t) the voltages of the grid sides a, b and c of the offshore wind farm collection station, I a (t)、I b (t) and I c And (t) the currents of the network side a, the network side b and the network side c of the offshore wind farm are respectively shown, and subscripts 1 to m respectively represent 1 to m ports.
13. The offshore wind power grid-tied flexible system impedance determination system according to claim 10, wherein the phase-sequence transformation module performs operations comprising:
time synchronization is carried out on voltage and current waveforms of different ports based on a recorder GPS time signal;
selecting time section t under resonance working condition h In f with S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf h -1/(2Δf),t h +1/(2Δf)]Wherein f is S The original signal sampling frequency is adopted, and delta f is the frequency spectrum resolution; windowing the electric quantity of the port at the side of the offshore AC network of the flexible direct system and the port at the side of the network of the offshore wind farm collection station to obtain Fourier transform of the electric quantity of the port at the side of the offshore AC network of the flexible direct system, and obtaining Fourier spectrum M of the voltages of a phase, a phase and a phase of the offshore AC network of the flexible direct system USa (f h )、M USb (f h ) And M USc (f h ) Obtaining a Fourier spectrum M of phase currents a, b and c at the side of the marine alternating current network of the flexible direct system ISa (f h )、M ISb (f h ) And M ISc (f h ) Fourier spectrum M of voltages of a, b and c at grid side of offshore wind farm collection station Ua (f h )、M Ub (f h ) And M Uc (f h ) And offshore wind farm collectionFourier spectrum M of phase currents a, b and c at substation network side Ia (f h )、M Ib (f h ) And M Ic (f h )；
Performing phase sequence transformation on the electric quantity resonance frequency component of each port based on the 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 ) Positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct offshore alternating current network side system in a complex expression form at the resonant frequency; m IS1 (f h )、M IS2 (f h )、M IS0 (f h ) The method comprises the following steps that positive sequence, negative sequence and zero sequence components of the port current of the marine AC network side in a complex expression form are obtained; m U1 (f h )、M U2 (f h )、M U0 (f h ) The positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in the form of complex expression at the resonant frequency; m I1 (f h )、M I2 (f h )、M I0 (f h ) The method comprises the steps that positive sequence, negative sequence and zero sequence components of the network side port current of the offshore wind farm collection station in a complex expression form at resonance frequency are obtained;
selecting time section t under steady state working condition o And t with h The interval time is 1/f h Integer multiple of f S The window function g (t) =1, t = [ t ] for the analysis window structure square wave signal,/deltaf o -1/(2Δf),t o +1/(2Δf)]Windowing the electric quantity of the side port of the offshore AC network of the flexible direct system and the side port of the network of the offshore wind farm collection station to obtain Fourier transform of the voltage of a phase, b phase and c phase of the offshore AC network of the flexible direct system
And
obtaining phase current Fourier spectrums of a, b and c sides of an offshore alternating current network of the flexible direct current system
And with
And obtaining a Fourier spectrum of voltages of a, b and c phases at the grid side of the offshore wind power plant collection station
And
similarly, fourier spectrums of currents of a, b and c at net side of offshore wind power plant collecting station are obtained
And with
The phase sequence conversion is carried out on the electric quantity resonance frequency component of each port as follows:
wherein the content of the first and second substances,
the positive sequence, negative sequence and zero sequence components of the port voltage of the flexible direct system offshore alternating current network side in the form of complex expression at the resonant frequency;
positive sequence, negative sequence and zero sequence components of the cross network side port current on the sea in the flexible-straight system in a complex expression form at the resonant frequency;
positive sequence, negative sequence and zero sequence components of the network side port voltage of the offshore wind farm collection station in a complex expression form at the resonant frequency;
the system comprises positive sequence, negative sequence and zero sequence components of the network side port current of the offshore wind farm collection station in a complex expression form at the resonant frequency.
14. The offshore wind power through-grid-flexible system impedance determination system according to claim 12, wherein the equation building module performs operations comprising:
aiming at the resonant frequency, calculating pi-type equivalent circuit parameters of the submarine cable under the resonant frequency; equating m wind power plants to harmonic current source i Vi And harmonic impedance z Vi A parallel connection mode, wherein a subscript i is a wind power plant number; equating the ports on the offshore alternating current network side of n flexible direct systems as harmonic voltage sources u Mj And z Mj The harmonic impedance is connected in series, wherein a subscript j is the serial number of ports on the offshore alternating current network side of the flexible-direct system;
writing a circuit network equation according to kirchhoff current and voltage law sequence aiming at a real system topological structure before resonance;
y = F for positive sequence networks 1 (X)，F 1 For nonlinear circuit equation, selecting positive sequence component of electric quantity
Is a function value of u in the formula 1,1 (f h ),…,u m,1 (f h ) And u S1,1 (f h ),…,u Sn,1 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,1 (f h ),…,i m,1 (f h ) And i S1,1 (f h ),…,i Sn,1 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each impedance component to be determined in positive sequence
For unknown variables, in which 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, i, of the net side port of the 1 st to m offshore wind farm collection station and the offshore alternating current net side port of the 1 st to n flexible and straight system V1,1 (f h ),…,i Vm,1 (f h ) And u M1,1 (f h ),…,u Mn,1 (f h ) Respectively providing 1-m offshore wind farm collection station port equivalent positive sequence harmonic current sources and 1-n flexible direct system offshore alternating current network side port equivalent positive sequence harmonic voltage sources;
y = F for negative sequence network 2 (X)，F 2 For nonlinear circuit equation, selecting negative sequence component of electric quantity
Is a function value of u in the formula 1,2 (f h ),…,u m,2 (f h ) And u S1,2 (f h ),…,u Sn,2 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,2 (f h ),…,i m,2 (f h ) And i S1,2 (f h ),…,i Sn,2 (f h ) Respectively providing a positive sequence harmonic current component source for the network side port of the collection station of the 1 st to m offshore wind farm and a positive sequence harmonic current component for the offshore alternating current network side port of the 1 st to n flexible and direct system; each to-be-determined negative sequence impedance component
For unknown variables, in which z V1,2 (f h ),…,z Vm,2 (f h ) And z M1,2 (f h ),…,z Mn,2 (f h ) Equivalent negative sequence impedance, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n offshore alternating current network side ports of the flexible and direct systems respectively V1,2 (f h ),…,i Vm,2 (f h ) And u M1,2 (f h ),…,u Mn,2 (f h ) Respectively 1 st to m offshore wind power plantsThe equivalent negative sequence harmonic current source at the port of the collecting station and the equivalent negative sequence harmonic voltage source at the side port of the marine alternating current network of the 1 st to nth flexible direct systems;
y = F for zero sequence network 0 (X)，F 0 Selecting zero-sequence component of electric quantity to form nonlinear circuit equation
Is a function value of u in the formula 1,0 (f h ),…,u m,0 (f h ) And u S1,0 (f h ),…,u Sn,0 (f h ) Respectively are positive sequence harmonic voltage components i of net side ports of 1 st to m offshore wind farm collection stations and 1 st to n flexible and straight system offshore AC net side ports 1,0 (f h ),…,i m,0 (f h ) And i S1,0 (f h ),…,i Sn,0 (f h ) Respectively providing a positive sequence harmonic current component source for a network side port of a collection station of the 1 st to m offshore wind power plants and a positive sequence harmonic current component for a network side port of an offshore alternating current network of the 1 st to n flexible and straight systems; each to-be-solved zero sequence impedance component
For unknown variables, in which 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, i, of the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports V1,0 (f h ),…,i Vm,0 (f h ) And u M1,0 (f h ),…,u Mn,0 (f h ) The equivalent zero-sequence harmonic current sources are respectively the 1 st to m offshore wind farm collection station ports and the 1 st to n flexible direct system offshore alternating current network side ports.
15. The offshore wind power grid-tied system impedance determination system according to claim 14, wherein the equation initial value calculation module performs the following operations:
aiming at the actual system topological structure before resonance, substituting the harmonic component of the offshore wind farm collection station port current under the normal working condition as an offshore wind farm collection station port equivalent harmonic current source, taking the harmonic component of the flexible and straight system offshore current network side port voltage under the steady working condition as a flexible and straight system offshore current network side port equivalent harmonic voltage source, and enabling the flexible and straight system offshore current network side port equivalent harmonic voltage source to be connected with the harmonic component
Writing a positive sequence, a negative sequence and a zero sequence network equation Y of a circuit according to kirchhoff current and voltage law 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) )，F 1 (o) 、F 2 (o) And F 0 (o) Is a non-linear circuit equation and is,
and
is the function value of the function value,
and
is an unknown variable;
X 1 (o) 、X 2 (o) and X 0 (o) Solving a nonlinear equation set Y by taking a typical impedance characteristic parameter of a wind power plant and a flexible direct system as an initial value 1 (o) ＝F 1 (o) (X 1 (o) )、Y 2 (o) ＝F 2 (o) (X 2 (o) ) And Y 0 (o) ＝F 0 (o) (X 0 (o) ) And the solution result is marked as X 1 (1) 、X 2 (1) And X 0 (1) 。
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