Method for measuring equivalent admittance of grid-connected inverter under condition of unknown power grid impedance
阅读说明：本技术 在电网阻抗未知的情况下测量并网逆变器等效导纳的方法 (Method for measuring equivalent admittance of grid-connected inverter under condition of unknown power grid impedance ) 是由 杜雄 刘俊良 张博 杜程茂 孙鹏菊 罗全明 于 2019-09-18 设计创作，主要内容包括：本发明提供一种在电网阻抗未知的情况下测量并网逆变器等效导纳的方法,属于新能源并网领域。在真实的测量场景中,逆变器的阻抗受电网阻抗影响,传统的测量方法在电网阻抗已知时获取逆变器的阻抗,但现实的测量场景中,电网阻抗往往是未知的。于是,本发明提供电网阻抗未知的情况下,通过六组测量信息,建立数学模型,求解出并网逆变器自身的特征导纳Y<Sub>SA</Sub>、<Image he="81" wi="179" file="DDA0002206048480000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>和<Image he="82" wi="105" file="DDA0002206048480000012.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>并用特征导纳来确定逆变器的等效导纳。本发明考虑了电网阻抗与逆变器阻抗之间的相互影响,同时避免同步相位角的引入,测量精度高。(the invention provides a method for measuring equivalent admittance of a grid-connected inverter under the condition of unknown power grid impedance, and belongs to the field of new energy grid connection. In a real measurement scenario, the impedance of the inverter is affected by the impedance of the power grid, and the impedance of the inverter is obtained by a traditional measurement method when the impedance of the power grid is known, but in a real measurement scenario, the impedance of the power grid is often unknown. Therefore, under the condition that the power grid impedance is unknown, the method establishes a mathematical model through six groups of measurement information, and solves the characteristic admittance Y of the grid-connected inverter SA 、 And And using the characteristic admittance to determine an equivalent admittance of the inverter. The invention considers the mutual influence between the power grid impedance and the inverter impedance, avoids the introduction of a synchronous phase angle and has high measurement precision.)
1. AA method for measuring equivalent admittance of a grid-connected inverter under the condition of unknown power grid impedance is characterized in that: the method comprises the following steps: equivalent admittance Y of grid-connected inverterINVThe following method is adopted for determination:
Wherein, YINV(fP) Indicating the equivalent admittance, Y, of the inverter in the inverter grid-connected systemSA(fp) Representing a frequency fPThe mutual admittance of the two optical fibers is determined,Representing a frequency of 2f0-fPThe mutual admittance after the conjugation of (a) and (b),Representing the product of the self-admittance and its conjugate at different frequencies,Representing a frequency of 2f0-fPThe conjugated grid impedance;
Wherein, YSA(fp)、AndDetermined by simultaneous equations (2) to (4),
wherein, YSA(fp) Representing a frequency fPThe mutual admittance of the two optical fibers is determined,Representing frequencyIs 2f0-fPThe mutual admittance after the conjugation of (a) and (b),Denotes the product of the self-admittance and its conjugate at different frequencies, Ip(fp) Representing the measured positive sequence response current, Vp(fp) Representing the measured positive sequence response voltage,Representing a frequency of 2f0-fPThe impedance of the network after the conjugation of (c),Denotes the frequency 2f after conjugation0-fPThe measured positive sequence response current is measured in response to the current,denotes the frequency 2f after conjugation0-fPmeasured positive sequence response voltage, Zg(fp) Representing a frequency fPOf the network impedance, Ip1(fp) Representing access test impedance ZtestPositive sequence response current, V, measured afterp1(fp) Representing access test impedance ZtestThe positive sequence response voltage of the post-measurement,Is shown at 2f0-fPAnd the sum of the test impedance after lower conjugation and the impedance of the power grid.
2. The method for measuring the equivalent admittance of the grid-connected inverter under the condition of unknown grid impedance according to claim 1, wherein: the frequency is 2f0-fPThe conjugated network impedance ofIt is determined by the following method,
wherein the content of the first and second substances,representing a frequency of 2f0-fPThe impedance of the network after the conjugation of (c),Denotes post-conjugate 2f measured on the grid side0-fPthe positive sequence response voltage at the frequency,Denotes the frequency 2f after conjugation0-fPa measured positive sequence response current;
Said frequency is fPOf the network impedance Zg(fp) It is determined by the following method,
Wherein Z isg(fp) Representing a frequency fPOf the network impedance, Vt,p(fp) Indicating the positive sequence response voltage, I, measured on the grid sidep(fp) Represents the measured positive sequence response current;
The frequency 2f0-fPsum of test impedance and grid impedance after lower conjugationIt is determined by the following method,
Wherein the content of the first and second substances,Representing a frequency 2f0-fPthe sum of the lower conjugated test impedance and the grid impedance,representing access test impedance ZtestFrequency of 2f measured on the rear grid side0-fPThe positive sequence is responsive to the voltage in response,Denotes the frequency 2f after conjugation0-fPThe measured positive sequence response current.
3. The method for measuring the equivalent admittance of the grid-connected inverter under the condition of unknown grid impedance according to claim 2, wherein:
The measured positive sequence response current Ip(fp) The following method is adopted for determination:
wherein, Ip(fp) Representing the measured positive sequence response current, IaRepresents the alternating current phase A current, IbRepresents alternating current phase B current;
The measured positive sequence response voltage Vp(fp) The following method is adopted for determination:
wherein, Vp(fp) Indicating the measured positive sequence response voltage, VabRepresenting the voltages of the A-phase and B-phase AC lines, Vbcrepresenting the voltages of the phase B and the phase C of the alternating current;
The access test impedance ZtestPost-measured positive sequence response current Ip1(fp) The following method is adopted for determination:
Wherein, Ip1(fp) Representing access test impedance Ztestpost-measured positive sequence response current, Ia,1Representing access test impedance Ztestrear A phase current, Ib,1representing access test impedance ZtestThe rear B-phase current;
The access test impedance Ztestpositive sequence response voltage V of post-measurementp1(fp) The following method is adopted for determination:
wherein, Vp1(fp) Representing access test impedance ZtestPositive sequence response voltage, V, measured afterab，1Representing access test impedance ZtestThe voltage of A phase and B phase line, V, of side AC of rear inverterbc,1representing access test impedance ZtestThe alternating current of the rear inverter is the voltages of the phase B and the phase C;
The positive sequence response voltage V measured at the grid sidet,p(fp) The following method is adopted for determination:
Wherein, Vt,p(fp) Indicating the positive sequence response voltage, V, measured on the grid sideab，tRepresenting the voltages of phase A and phase B, V, of the AC current at the side of the gridbcLine voltages representing alternating current phases B and C;
The access test impedance ZtestPositive sequence response voltage V measured at back power grid sidet1,p(fp) The following method is adopted for determination:
wherein, Vt1,p(fp) Representing access test impedance Ztestpositive sequence response voltage, V, measured at the rear grid sideab,t1Representing access test impedance ZtestThe voltage of A phase and B phase line of back power grid side ACbc，1representing the voltages of the phase B and the phase C of the alternating current on the side of the power grid after the test impedance Ztest is accessed;
The frequency after conjugation 2f0-fPmeasured positive sequence response currentBy the pair Ip(2f0-fp) And (3) taking conjugation to determine:
Wherein, Ip(2f0-fp) The following method is adopted for determination:
Wherein, Ip(2f0-fp) Representing a frequency 2f0-fPMeasured positive sequence response current, Ip(fp,γ-l) And Ip(fp,l-δ) Representing the measured positive sequence response current at different frequencies, γ ═ δ +1,f0 denotes the grid power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
the frequency after conjugation 2f0-fPMeasured positive sequence voltageBy pairs of Vp(2f0-fp) The conjugate is taken for determination,
Wherein, Vp(2f0-fp) The following method is adopted for determination:
Wherein, Vp(2f0-fp) Representing a frequency 2f0-fPMeasured positive sequence voltage, Vp(fp,γ-l) And Vp(fp,l-δ) Representing the measured positive sequence response voltage at different frequencies, γ ═ δ +1,f0Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
Said post-conjugation 2f measured on the grid side0-fPpositive sequence response voltage at frequencyby pairs of Vt,p(2f0-fp) The conjugate is taken for determination,
Wherein, Vt,p(2f0-fp) The following method is adopted for determination:
wherein, Vt,p(2f0-fp) Indicating measurement of frequency 2f on the grid side0-fPPositive sequence response voltage, Vt,p(fp,γ-l) And Vt,p(fp,l-δ) Representing the positive sequence response voltage measured at different frequencies on the grid side, γ ═ δ +1,f0Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
The access test impedance ZtestThe conjugate back frequency measured at the back grid side is 2f0-fPpositive sequence response voltageBy pairs of Vt1,p(2f0-fp) Determining by taking the conjugate, wherein Vt1,p(2f0-fp) The following method is adopted for determination:
wherein, Vt1,p(2f0-fp) Representing access test impedance Ztestfrequency of 2f measured on the rear grid side0-fPpositive sequence response voltage, Vt1,p(fp,γ-l) And Vt1,p(fp,l-δ) Representing access test impedance Ztestthe response voltages of different frequencies, measured on the rear grid side, γ ═ δ +1,f0Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}。
4. The method for measuring the equivalent admittance of the grid-connected inverter under the condition of unknown grid impedance according to claim 3, wherein: and the voltage and the current are phase currents or line voltages measured after disturbance is injected at a common coupling point of the grid-connected system.
5. The method of measuring grid-connected inverter equivalent admittance under the condition of unknown grid impedance according to claim 4, wherein: the frequency of the injected disturbance is an arithmetic series, aTolerance d of the above-mentioned arithmetic progression is 2fp,1Wherein f isp,1Disturbance frequency, f, for first injectionp＝{fp,1,fp,2...fp,l...fp,n-1,fp,nand satisfyWherein δ is a positive integer.
6. The method for measuring the equivalent admittance of the grid-connected inverter under the condition of unknown grid impedance according to claim 3, wherein: the test impedance ZtestAnd the public coupling points are connected in series to a grid-connected inverter grid-connected system.
Technical Field
the invention relates to the field of new energy grid connection, in particular to a method for measuring equivalent admittance of a grid-connected inverter under the condition of unknown power grid impedance.
Background
In recent years, environmental deterioration, climate warming, exhaustion of fossil fuels, and the like have led governments around the world to vigorously develop new renewable energy sources. At present, new energy resources represented by wind power and photovoltaic are vigorously developed. By the end of 2018, the installed capacity of wind power and wind power is 1.84 hundred million kilowatts and the installed capacity of photovoltaic power generation is 1.74 hundred million kilowatts in China. Both new and cumulative installed capacity continue to be world-first. New energy grid connection easily impacts grid stability, for example, 25Hz and 75Hz harmonic oscillation occurs in a Xinjiang Hami wind power base in 2015, three thermal power generating units beyond hundreds of kilometers are caused to protect the action generator tripping, and the power loss is 150 kilo kW. The new energy grid-connected system is different from the traditional grid-connected system, and the difference is that: the conventional grid-connected system is dominated by passive equipment, and the new energy grid-connected system is dominated by active equipment, wherein the active equipment is mainly represented by an inverter. However, the grid-connected inverter has strong nonlinear characteristics, which causes frequent harmonic oscillation and causes system instability. Therefore, in order to analyze the stability of such inverter grid-connected system, the third-generation teaching proposes an impedance analysis method. The system is divided into source impedance and load impedance, the stability of the system is analyzed according to the ratio of the two impedances, and the stability of the system is judged by analyzing whether a Nyquist curve of the ratio of the inverter impedance to the grid impedance surrounds a point (-1,0) or not by taking an inverter grid-connected system as an example. The impedance analysis method has been successfully applied to harmonic oscillation in the hami region of Xinjiang. In order to analyze the stability of the inverter grid-connected system, the impedance of the inverter is important to obtain, but in the process of measuring the impedance of the grid-connected inverter, the impedance of a target power grid is often in an unknown state.
therefore, a measurement method capable of accurately measuring the inverter impedance when the grid impedance is unknown is needed.
Disclosure of Invention
In view of this, the present invention provides a method for measuring the equivalent admittance of a grid-connected inverter under the condition that the grid impedance is unknown.
The invention provides a method for measuring equivalent admittance of a grid-connected inverter under the condition of unknown power grid impedance, which is characterized by comprising the following steps: the method comprises the following steps: equivalent admittance Y of grid-connected inverterINVthe following method is adopted for determination:
Wherein, YINV(fP) Indicating the equivalent admittance, Y, of the inverter in the inverter grid-connected systemSA(fp) Representing a frequency fPThe mutual admittance of the two optical fibers is determined,Representing a frequency of 2f0-fPThe mutual admittance after the conjugation of (a) and (b),Representing the product of the self-admittance and its conjugate at different frequencies,Representing a frequency of 2f0-fPThe conjugated grid impedance;
Wherein, YSA(fp)、AndDetermined by simultaneous equations (2) to (4),
wherein, YSA(fp) Representing a frequency fPThe mutual admittance of the two optical fibers is determined,Representing a frequency of 2f0-fPThe mutual admittance after the conjugation of (a) and (b),denotes the product of the self-admittance and its conjugate at different frequencies, Ip(fp) Representing the measured positive sequence response current, Vp(fp) Representing the measured positive sequence response voltage,representing a frequency of 2f0-fPThe impedance of the network after the conjugation of (c),denotes the frequency 2f after conjugation0-fPThe measured positive sequence response current is measured in response to the current,denotes the frequency 2f after conjugation0-fPMeasured positive sequence response voltage, Zg(fp) Representing a frequency fPof the network impedance, Ip1(fp) Representing access test impedance ZtestPositive sequence response current, V, measured afterp1(fp) Representing access test impedance ZtestThe positive sequence response voltage of the post-measurement,is shown at 2f0-fPAnd the sum of the test impedance after lower conjugation and the impedance of the power grid.
further, the frequency is 2f0-fPThe conjugated network impedance ofit is determined by the following method,
Wherein the content of the first and second substances,Representing a frequency of 2f0-fPThe impedance of the network after the conjugation of (c),Denotes post-conjugate 2f measured on the grid side0-fPThe positive sequence response voltage at the frequency,Denotes the frequency 2f after conjugation0-fPA measured positive sequence response current;
said frequency is fPOf the network impedance Zg(fp) It is determined by the following method,
Wherein Z isg(fp) Representing a frequency fPOf the network impedance, Vt,p(fp) Indicating the positive sequence response voltage, I, measured on the grid sidep(fp) Represents the measured positive sequence response current;
The frequency 2f0-fPSum of test impedance and grid impedance after lower conjugationIt is determined by the following method,
Wherein the content of the first and second substances,Representing a frequency 2f0-fPThe sum of the lower conjugated test impedance and the grid impedance,Representing access test impedance ZtestFrequency of 2f measured on the rear grid side0-fPThe positive sequence is responsive to the voltage in response,Denotes the frequency 2f after conjugation0-fPThe measured positive sequence response current.
Further, the measured positive sequence response current Ip(fp) The following method is adopted for determination:
Wherein, Ip(fp) Representing the measured positive sequence response current, IaRepresents the alternating current phase A current, IbRepresents alternating current phase B current;
The measured positive sequence response voltage Vp(fp) The following method is adopted for determination:
Wherein, Vp(fp) Indicating the measured positive sequence response voltage, Vabrepresenting the voltages of the A-phase and B-phase AC lines, Vbcrepresenting the voltages of the phase B and the phase C of the alternating current;
The access test impedance ZtestPost-measured positive sequence response current Ip1(fp) The following method is adopted for determination:
Wherein, Ip1(fp) Representing access test impedance ZtestPost-measured positive sequence response current, Ia,1Representing access test impedance ZtestRear A phase current, Ib,1Representing access test impedance ZtestThe rear B-phase current;
The access test impedance ZtestPositive sequence response voltage V of post-measurementp1(fp) The following method is adopted for determination:
Wherein, Vp1(fp) Representing access test impedance Ztestpositive sequence response voltage, V, measured afterab，1Representing access test impedance ZtestThe voltage of A phase and B phase line, V, of side AC of rear inverterbc,1representing access test impedance Ztestthe alternating current of the rear inverter is the voltages of the phase B and the phase C;
The positive sequence response voltage V measured at the grid sidet,p(fp) The following method is adopted for determination:
Wherein, Vt,p(fp) Indicating the positive sequence response voltage, V, measured on the grid sideab，tRepresenting the voltages of phase A and phase B, V, of the AC current at the side of the gridbcline voltages representing alternating current phases B and C;
The access test impedance ZtestPositive sequence response voltage V measured at back power grid sidet1,p(fp) The following method is adopted for determination:
wherein, Vt1,p(fp) Representing access test impedance Ztestpositive sequence response voltage, V, measured at the rear grid sideab,t1representing access test impedance Ztestthe voltage of A phase and B phase line of back power grid side ACbc，1Representing the voltages of the phase B and the phase C of the alternating current on the side of the power grid after the test impedance Ztest is accessed;
The frequency after conjugation 2f0-fPMeasured positive sequence response currentBy the pair Ip(2f0-fp) And (3) taking conjugation to determine:
wherein, Ip(2f0-fp) The following method is adopted for determination:
Wherein, Ip(2f0-fp) Representing a frequency 2f0-fPMeasured positive sequence response current, Ip(fp,γ-l) And Ip(fp,l-δ) Representing the measured positive sequence response current at different frequencies, γ ═ δ +1,f0 denotes the grid power frequency, fprepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
the frequency after conjugation 2f0-fPMeasured positive sequence voltageBy pairs of Vp(2f0-fp) The conjugate is taken for determination,
Wherein, Vp(2f0-fp) The following method is adopted for determination:
wherein, Vp(2f0-fp) Representing a frequency 2f0-fPMeasured positive sequence voltage, Vp(fp,γ-l) And Vp(fp,l-δ) Indicating positive sequence of measurements at different frequenciesIn response to the voltage, γ ═ δ +1,f0Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
said post-conjugation 2f measured on the grid side0-fPPositive sequence response voltage at frequencyBy pairs of Vt,p(2f0-fp) The conjugate is taken for determination,
Wherein, Vt,p(2f0-fp) The following method is adopted for determination:
Wherein, Vt,p(2f0-fp) Indicating measurement of frequency 2f on the grid side0-fPPositive sequence response voltage, Vt,p(fp,γ-l) And Vt,p(fp,l-δ) Representing the positive sequence response voltage measured at different frequencies on the grid side, γ ═ δ +1,Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
The access test impedance ZtestThe conjugate back frequency measured at the back grid side is 2f0-fPPositive sequence response voltageby pairs of Vt1,p(2f0-fp) The conjugate is taken for determination,
wherein, Vt1,p(2f0-fp) The following method is adopted for determination:
Wherein, Vt1,p(2f0-fp) Representing access test impedance ZtestFrequency of 2f measured on the rear grid side0-fPpositive sequence response voltage, Vt1,p(fp,γ-l) And Vt1,p(fp,l-δ) Representing access test impedance Ztestthe response voltages of different frequencies, measured on the rear grid side, γ ═ δ +1,f0Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}。
further, the voltage and the current are phase currents or line voltages measured after disturbance is injected at a common coupling point of the grid-connected system.
further, the frequency of the injection disturbance is in an arithmetic progression, and the tolerance d of the arithmetic progression is 2fp,1Wherein f isp,1disturbance frequency, f, for first injectionp＝{fp,1,fp,2...fp,l...fp,n-1,fp,nAnd satisfywherein δ is a positive integer.
Further, the test impedance Ztestand the public coupling points are connected in series to a grid-connected inverter grid-connected system.
The invention has the beneficial technical effects that: compared with the existing inverter impedance measuring method of a rotating coordinate system (dq standard system), the method avoids the introduction of a synchronous phase angle, further avoids additional measuring errors and improves the measuring accuracy; compared with the existing sequence impedance measuring method, the method considers the existence of the power grid impedance in practice and considers the influence of the power grid impedance on the inverter impedance in a calculation model, and the impedance information of the inverter expressed by the measuring result is more accurate.
Drawings
The invention is further described below with reference to the following figures and examples:
Fig. 1 is a measurement setup diagram of the present invention.
FIG. 2 shows admittance Y of the present inventionSAbode plot of the measurements with the mathematical model.
FIG. 3 is an admittance of the present inventionbode plot of the measurements with the mathematical model.
FIG. 4 shows the present inventionbode plot of the measurements with the mathematical model.
FIG. 5 is a diagram of a laboratory measurement platform of the present invention.
FIG. 6 is a Bode plot of experimental measurements and mathematical models of the present invention.
Detailed Description
the invention is further described with reference to the accompanying drawings in which:
the invention provides a method for measuring equivalent admittance of a grid-connected inverter under the condition of unknown power grid impedance, which is characterized by comprising the following steps: the method comprises the following steps: equivalent admittance Y of grid-connected inverterINVThe following method is adopted for determination:
Wherein, YINV(fP) Indicating the equivalent admittance, Y, of the inverter in the inverter grid-connected systemSA(fp) Representing a frequency fPthe mutual admittance of the two optical fibers is determined,representing a frequency of 2f0-fPthe mutual admittance after the conjugation of (a) and (b),Representing the product of the self-admittance and its conjugate at different frequencies,Representing a frequency of 2f0-fPThe conjugated grid impedance;
Wherein, YSA(fp)、AndDetermined by simultaneous equations (2) to (4),
Wherein, YSA(fp) Representing a frequency fPthe mutual admittance of the two optical fibers is determined,Representing a frequency of 2f0-fPThe mutual admittance after the conjugation of (a) and (b),denotes the product of the self-admittance and its conjugate at different frequencies, Ip(fp) Representing the measured positive sequence response current, Vp(fp) Representing the measured positive sequence response voltage,Representing a frequency of 2f0-fPThe impedance of the network after the conjugation of (c),Denotes the frequency 2f after conjugation0-fPThe measured positive sequence response current is measured in response to the current,Denotes the frequency 2f after conjugation0-fPmeasured positive sequence response voltage, Zg(fp) Representing a frequency fPOf the network impedance, Ip1(fp) Representing access test impedance Ztestpositive sequence response current, V, measured afterp1(fp) Representing access test impedance ZtestThe positive sequence response voltage of the post-measurement,Is shown at 2f0-fPAnd the sum of the test impedance after lower conjugation and the impedance of the power grid. Compared with the existing inverter impedance measuring method of a rotating coordinate system (dq standard system), the method avoids the introduction of a synchronous phase angle, further avoids extra measuring errors and improves the measuring accuracy; compared with the existing sequence impedance measuring method, the method considers the existence of the power grid impedance in practice and considers the influence of the power grid impedance on the inverter impedance in a calculation model, and the impedance information of the inverter expressed by the measuring result is more accurate.
In this embodiment, the frequency is 2f0-fPThe conjugated network impedance ofIt is determined by the following method,
Wherein the content of the first and second substances,Representing a frequency of 2f0-fPThe impedance of the network after the conjugation of (c),Denotes post-conjugate 2f measured on the grid side0-fPThe positive sequence response voltage at the frequency,denotes the frequency 2f after conjugation0-fPa measured positive sequence response current;
Said frequency is fPOf the network impedance Zg(fp) It is determined by the following method,
Wherein Z isg(fp) Representing the grid impedance at frequency fP, Vt, p (fP) representing the positive sequence response voltage measured on the grid side, Ip(fp) Represents the measured positive sequence response current;
The frequency 2f0-fPSum of test impedance and grid impedance after lower conjugationit is determined by the following method,
Wherein the content of the first and second substances,Representing a frequency 2f0-fPThe sum of the lower conjugated test impedance and the grid impedance,Representing access test impedance ZtestFrequency of 2f measured on the rear grid side0-fPthe positive sequence is responsive to the voltage in response,denotes the frequency 2f after conjugation0-fPThe measured positive sequence response current. By the technical scheme, the phase voltage or line current after disturbance is measuredthereby determining the impedance of the target grid.
In this embodiment, the measured positive sequence response current Ip(fp) The following method is adopted for determination:
Wherein, Ip(fp) Representing the measured positive sequence response current, IaRepresents the alternating current phase A current, IbRepresents alternating current phase B current;
The measured positive sequence response voltage Vp(fp) The following method is adopted for determination:
Wherein, Vp(fp) Indicating the measured positive sequence response voltage, VabRepresenting the voltages of the A-phase and B-phase AC lines, VbcRepresenting the voltages of the phase B and the phase C of the alternating current;
The access test impedance Ztestpost-measured positive sequence response current Ip1(fp) The following method is adopted for determination:
Wherein, Ip1(fp) Representing access test impedance ZtestPost-measured positive sequence response current, Ia,1Representing access test impedance ZtestRear A phase current, Ib,1Representing access test impedance ZtestThe rear B-phase current;
The access test impedance ZtestPositive sequence response voltage V of post-measurementp1(fp) The following method is adopted for determination:
wherein, Vp1(fp) Representing access test impedance ZtestPositive sequence response voltage, V, measured afterab，1representing access test impedance ZtestThe voltage of A phase and B phase line, V, of side AC of rear inverterbc,1Representing access test impedance ZtestThe alternating current of the rear inverter is the voltages of the phase B and the phase C;
the positive sequence response voltage V measured at the grid sidet,p(fp) The following method is adopted for determination:
Wherein, Vt,p(fp) Indicating the positive sequence response voltage, V, measured on the grid sideab，trepresenting the voltages of phase A and phase B, V, of the AC current at the side of the gridbcLine voltages representing alternating current phases B and C;
The access test impedance ZtestPositive sequence response voltage V measured at back power grid sidet1,p(fp) The following method is adopted for determination:
Wherein, Vt1,p(fp) Representing access test impedance Ztestpositive sequence response voltage, V, measured at the rear grid sideab,t1Representing access test impedance Ztestthe voltage of A phase and B phase line of back power grid side ACbc，1representing the voltages of the phase B and the phase C of the alternating current on the side of the power grid after the test impedance Ztest is accessed;
The frequency after conjugation 2f0-fPMeasured positive sequence response currentby the pair Ip(2f0-fp) And (3) taking conjugation to determine:
wherein, Ip(2f0-fp) The following method is adopted for determination:
Wherein, Ip(2f0-fp) Representing a frequency 2f0-fPMeasured positive sequence response current, Ip(fp,γ-l) And Ip(fp,l-δ) Representing the measured positive sequence response current at different frequencies, γ ═ δ +1,f0 denotes the grid power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
The frequency after conjugation 2f0-fPMeasured positive sequence voltageBy pairs of Vp(2f0-fp) The conjugate is taken for determination,
Wherein, Vp(2f0-fp) The following method is adopted for determination:
wherein, Vp(2f0-fp) Representing a frequency 2f0-fPMeasured positive sequence voltage, Vp(fp,γ-l) And Vp(fp,l-δ) Representing the measured positive sequence response voltage at different frequencies, γ ═ δ +1,f0Representing grid-connection power frequency, fprepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
Said post-conjugation 2f measured on the grid side0-fPPositive sequence response voltage at frequencyBy pairs of Vt,p(2f0-fp) The conjugate is taken for determination,
Wherein, Vt,p(2f0-fp) The following method is adopted for determination:
Wherein, Vt,p(2f0-fp) Indicating measurement of frequency 2f on the grid side0-fPpositive sequence response voltage, Vt,p(fp,γ-l) And Vt,p(fp,l-δ) Representing the positive sequence response voltage measured at different frequencies on the grid side, γ ═ δ +1,f0Representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}；
The access test impedance ZtestThe conjugate back frequency measured at the back grid side is 2f0-fPPositive sequence response voltageBy pairs of Vt1,p(2f0-fp) The conjugate is taken for determination,
wherein, Vt1,p(2f0-fp) The following method is adopted for determination:
wherein, Vt1,p(2f0-fp) Representing access test impedance Ztestfrequency of 2f measured on the rear grid side0-fPPositive sequence response voltage, Vt1,p(fp,γ-l) And Vt1,p(fp,l-δ) Representing access test impedance ZtestThe response voltages of different frequencies, measured on the rear grid side, γ ═ δ +1,f0representing grid-connection power frequency, fpRepresenting the frequency of the injected perturbation voltage,
fp＝{fp,1,fp,2...fp,l...fp,n-1,fp,n}。
in the embodiment, the voltage and the current are phase currents or line voltages measured after disturbance is injected at a common coupling point of the grid-connected system. As shown in fig. 5 and fig. 1, the phase current or the line voltage is measured after a disturbance is injected at a common coupling point of the grid-connected system, and the positive and negative sequence decomposition is performed on the measured phase current and line voltage.
In this embodiment, the frequency of the injection disturbance is an arithmetic progression, and the tolerance d of the arithmetic progression is 2fp,1Wherein f isp,1Disturbance frequency, f, for first injectionp＝{fp,1,fp,2...fp,l...fp,n-1,fp,nAnd satisfyWherein δ is a positive integer. In this embodiment, setting the disturbance frequency to be equal-difference series can save the measurement time, the full frequency band is not injected with each frequency, and the phase current or phase voltage of some disturbance frequencies can be obtained by calculation, for example, by accessing the test impedance Ztestfrequency of 2f measured on the rear grid side0-fPPositive sequence response voltage Vt1,p(2f0-fp) The impedance Z can be tested by accesstestDifferent frequencies V measured at the rear grid sidet1,p(fp,γ-l) Or Vt1,p(fp,l-δ) The response voltage is calculated, and therefore field test time is saved.
in this embodiment, the test impedance Ztestin series connectionAnd accessing a common coupling point of the grid-connected inverter grid-connected system. The test impedance is connected in series, the influence on the self characteristic of the power grid impedance is small, the tested system is easier to stabilize, and the stability of the power grid is not influenced during testing.
First according to d-2 fp,1AndSetting the frequency of the disturbance injection, e.g. delta 10, fp，15 Hz. After injecting single-phase voltage disturbance under set frequency, measuring voltage Vab、Vbcand Vab，twhile measuring the current Ia、Ib. When connected to test impedance ZtestThen, the measured voltage and current information is Vab1、Vbc1、Vab，t1、Ia1and Ib1. Obtaining current and voltage information I under positive and negative sequence decomposition by using formulas (8) to (17)p、Ip1、VP、VP1、Vt，Pand Vt1，Psubstituting the measured current and voltage information into the power grid impedance equation, and calculating to obtain the power grid impedanceSimultaneously, measured current and voltage information is substituted into equations (2) to (4), so that the measured information can be used to solve for the admittance YSA(fp)、Andsimultaneously adding YSA(fp)、AndAndsubstituting the formula (1) to determine the equivalent admittance Y of the grid-connected inverterINV(fP). FIG. 2 shows YSAThe measured values are compared to the mathematical model, the circles representing the measured values and the solid lines representing the mathematical model. FIG. 3 and FIG. 4 show the sameAndthe dots represent measured values and the solid lines represent mathematical models. As can be seen from fig. 2 to fig. 4, the measured value is particularly well matched with the mathematical model, and the equivalent admittance accuracy of the grid-connected inverter determined by the invention is high.
fig. 5 shows a measurement apparatus of a practical platform, which simulates a real power grid using an ac power supply and an inductor, and a network analyzer is a measurement device. Obtaining Y from actual measurement dataSA、andUsing equation (1), the equivalent admittances at two different grid inductances are obtained, as shown in fig. 6. FIG. 6(a) shows the grid inductance LgFig. 6(b) shows the grid inductance L as 3mHg5.1 mH. Also, the solid line is a mathematical model of the equivalent admittance, and the dots are the experimental measurements of the equivalent admittance. From fig. 6, it can be seen that the agreement between the experimental measurement values and the mathematical model is high.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：移动式多功能接地装置测试系统