CN113193598A - New energy grid-connected inverter transient stability margin evaluation method - Google Patents

New energy grid-connected inverter transient stability margin evaluation method Download PDF

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CN113193598A
CN113193598A CN202110604445.0A CN202110604445A CN113193598A CN 113193598 A CN113193598 A CN 113193598A CN 202110604445 A CN202110604445 A CN 202110604445A CN 113193598 A CN113193598 A CN 113193598A
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new energy
fault
connected inverter
energy grid
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CN113193598B (en
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姚骏
黄森
裴金鑫
陈诗玥
曹俊英
陈朝阳
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Chongqing University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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Abstract

The invention discloses a new energy grid-connected inverter transient stability margin evaluation method, which is used for converting a three-phase voltage signal of a grid-connected point to obtain two-phase direct current quantityU td、U tqAnd will beU tqAs an input signal for a phase locked loop; sequentially calculating the output angular frequency of the phase-locked loop and the transient stability margin of the inverter switched from the normal operation stage to the fault continuation stage、Equivalent limit cut angle、The equivalent limit removal time is compared with the actual fault detection delay, and whether the fault is unstable or not can be judged by switching from the normal operation stage to the fault continuous stage; and if the transient state is not unstable, calculating the transient state stability margin in the fault continuous stage and judging whether the transient state is unstable or not. And after the fault is cleared, calculating the transient stability margin switched from the fault continuous stage to the fault recovery stage and judging whether the transient stability margin is unstable or not. The method can judge whether the new energy grid-connected inverter is in different fault stages or notTransient instability occurs and a transient stability margin value is quantitatively calculated.

Description

New energy grid-connected inverter transient stability margin evaluation method
Technical Field
The invention relates to a transient stability margin evaluation method for a new energy grid-connected inverter, which is suitable for the new energy grid-connected inverter under the symmetrical short-circuit fault of an alternating current power grid.
Background
With the rapid increase of installed capacity of power generation of new energy sources such as wind energy, photovoltaic and the like, the permeability level of the new energy sources is continuously improved, but the new energy sources and loads are often in a serious reverse distribution characteristic, and a large-scale new energy power generation base is usually located in a remote area and has small short-circuit capacity. When an alternating current power grid has a serious short-circuit fault, the new energy grid-connected inverter is very likely to have a transient instability phenomenon, even a large-scale new energy base is disconnected, and the safe and stable operation of the power grid is seriously influenced. Therefore, the problem that the transient stability margin of the new energy grid-connected inverter during the short-circuit fault of the power grid can be quantitatively evaluated is a key problem in the development of the new energy power generation technology at present. Currently, scholars at home and abroad have carried out a series of related researches, such as the following published documents:
[1] transient stability analysis of the whole power conversion wind turbine generator set of the zham, chuasaxu and lie [ J ]. China Motor engineering report, 2017,37(14): 4018-.
[2]Jinxin Pei,JunYao,Ruikuo Liu,et al.Characteristic analysis andrisk assessment for Voltage-frequency coupled transient instability oflarge-scale grid-connected renewable energy plants during LVRT[J].IEEE Transactions on Industrial Electronics,2020,67(07):5515-5530。
The document [1] analyzes the influence of factors such as power grid strength, fault point port characteristics and phase-locked loop bandwidth on the transient stability margin of the new energy grid-connected inverter by using an equal area criterion, and provides a method for improving the transient stability margin of the new energy grid-connected inverter by reducing the phase-locked loop bandwidth, but the document does not quantize the transient stability margin. Document [2] utilizes a vector diagram analysis method to analyze the power grid voltage drop degree, an active reactive current instruction of a wind power grid-connected system and transmission line impedance from the perspective of voltage vector amplitude-frequency coupling, which are main reasons influencing transient synchronization stability of the wind power grid-connected system, and provides a method for evaluating a line resistance pressure drop angle margin, which quantitatively evaluates the transient stability margin of the system, but the method only aims at a fault duration stage and is difficult to evaluate the transient synchronization stability of the fault full stage. Actually, the transient response of the new energy grid-connected inverter in the whole fault process can be divided into different stages, and the transient stability margin of each stage needs to be quantitatively evaluated.
Disclosure of Invention
In view of the above disadvantages in the prior art, an object of the present invention is to provide a transient stability margin evaluation method for a new energy grid-connected inverter at different fault stages, where the method can determine whether a transient instability of the new energy grid-connected inverter occurs at different fault stages, and quantitatively calculate a transient stability margin value of the new energy grid-connected inverter.
The technical scheme of the invention is realized as follows:
a new energy grid-connected inverter transient stability margin evaluation method is used for judging the transient stability of the new energy grid-connected inverter in different fault stages, and is characterized in that: the method comprises the following specific steps:
A1) the new energy grid-connected inverter adopts a generator routine and utilizes a grid voltage d-axis orientation mode to acquire a grid-connected point three-phase voltage signal UtConverting the three-phase static coordinate system into a two-phase rotating coordinate system to obtain two-phase direct current quantity Utd、Utq；
A2) Will UtqAs an input signal of the phase-locked loop, the phase-locked loop output angular frequency ω is calculated according to the following formulaPLL：
ωPLL＝kppUtq+kip∫Utqdt+ωg
Wherein k isppAnd kipProportional and integral coefficients, omega, of the phase-locked loop, respectivelygIs the grid angular frequency rating;
A3) on the basis of the step A2), quantifying the transient stability margin of the new energy grid-connected inverter switched from the normal operation stage to the fault continuation stage according to the following formula:
Figure BDA0003093871580000021
wherein S isacc1、Sdec1And
Figure BDA0003093871580000026
respectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter switched from the normal operation stage to the fault continuation stage; delta d axis of phase-locked loop coordinate system and power grid voltage UgThe phase angle difference of (1), namely the equivalent power angle; delta0Is the equivalent power angle, delta, of the new energy grid-connected inverter at the initial moment of the fault detection stage1Is the equivalent power angle, delta, of the new energy grid-connected inverter at the initial moment of the fault duration stagemax1The upper limit value omega of the equivalent power angle of the new energy grid-connected inverter in the fault continuation stagebIs the angular frequency base value, UgfIs the voltage amplitude of the grid fault point, LgAnd RgRespectively the equivalent inductance and resistance of the point-to-point transmission line,
Figure BDA0003093871580000022
and
Figure BDA0003093871580000023
respectively an active current instruction and a reactive current instruction during low voltage ride through of the new energy grid-connected inverter, IdmFor the current limiting value, S, of the grid-side converter (GSC) of the new energy grid-connected inverternmThe value is a transient stability margin evaluation value of switching the new energy grid-connected inverter from a normal operation stage to a fault continuation stage;
A4) according to the step A3), calculating the equivalent limit cut-off angle of the new energy grid-connected inverter according to the following formula
Figure BDA0003093871580000024
Figure BDA0003093871580000025
A5) Obtained according to step A4)
Figure BDA0003093871580000031
Calculating the fault detection limit time of the new energy grid-connected inverter according to the following formula, namely equivalent limit removal time
Figure BDA0003093871580000032
Figure BDA0003093871580000033
A6) The transient stability criterion for switching the new energy grid-connected inverter from the normal operation stage to the fault continuation stage is as follows:
Figure BDA0003093871580000034
wherein, tdelayDelay for actual fault detection, if tdelayWhen the stability criterion is not met, the new energy grid-connected inverter generates a transient instability phenomenon;
A7) on the basis that the new energy grid-connected inverter meets the stability criterion obtained in the step A6), calculating the transient stability margin of the new energy grid-connected inverter in the fault continuation stage according to the following formula:
Figure BDA0003093871580000035
wherein S isacc2、Sdec2And
Figure BDA0003093871580000037
respectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter in the fault continuation stage; delta2Is a fault continuation phase omegaPLLAnd omegagWhen the equivalent power angle is equal, the equivalent power angle of the new energy grid-connected inverter is obtained; deltamin1The lower limit value delta of the equivalent power angle of the new energy grid-connected inverter in the fault continuation stagekAn equivalent power angle S corresponding to a balance working point of the new energy grid-connected inverter in the fault continuation stagedmThe value is the transient stability margin evaluation value S of the new energy grid-connected inverter in the fault continuation stagedmThe larger the system stability margin is, the higher the transient stability is;
A8) the transient stability criterion of the new energy grid-connected inverter in the fault continuation stage is as follows:
Figure BDA0003093871580000036
when the new energy grid-connected inverter meets the stability criterion, the new energy grid-connected inverter can smoothly reach and stably operate in a low-voltage ride-through control mode in a fault continuous stage;
A9) after the fault is cleared, the transient stability margin of the new energy grid-connected inverter switched from the fault continuous stage to the fault recovery stage can be quantified according to the following formula:
Figure BDA0003093871580000041
wherein S isacc3_4、Sdec4And
Figure BDA0003093871580000047
respectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter switched from the fault continuous stage to the fault recovery stage; delta4Is the equivalent initial power angle, delta, of the new energy grid-connected inverter in the fault recovery stageeIs the equivalent power angle, delta, corresponding to the balance working point of the new energy grid-connected inverter in the fault recovery stagemax2An upper limit value U of an equivalent power angle of the new energy grid-connected inverter at the fault recovery stagegnFor mains voltage rating, UtdnTo a point of grid connectionVoltage UtThe d-axis component of the nominal value,
Figure BDA0003093871580000042
is the power command value of the fault recovery stage; srmThe value is a transient stability margin evaluation value S of switching the new energy grid-connected inverter from a fault continuous stage to a fault recovery stagermThe larger the transient stability margin of the new energy grid-connected inverter is, the smaller the instability risk is;
A10) the transient stability criterion for switching the new energy grid-connected inverter from the fault continuous stage to the fault recovery stage is as follows:
Figure BDA0003093871580000043
when the new energy grid-connected inverter meets the stability criterion, the new energy grid-connected inverter can be successfully recovered to a stable operation state after the fault is cleared.
Compared with the prior art, the invention has the following beneficial effects:
the transient stability margin value of the new energy grid-connected inverter can be quantitatively calculated according to the power grid fault degree, the control characteristics and the operation condition of the new energy grid-connected inverter and the impedance of a power transmission line, can be used for transient instability criterion and transient stability margin evaluation of the new energy grid-connected inverter in different fault stages, and provides guiding suggestions for large-scale development of the new energy grid-connected inverter.
Drawings
Fig. 1 is a schematic diagram of fault stage division of a new energy grid-connected inverter.
Fig. 2 is a diagram illustrating a control structure of a typical pll.
The time domain simulation results of the new energy grid-connected inverter when the fault detection delay is 5ms and 10ms are respectively given by the working condition 1 and the working condition 2 in fig. 3.
Conditions 3 and 4 of FIG. 4 give current commands, respectively
Figure BDA0003093871580000044
And
Figure BDA0003093871580000045
Figure BDA0003093871580000046
and time domain simulation results of the new energy grid-connected inverter.
Conditions 5 and 6 of FIG. 5 give power commands, respectively
Figure BDA0003093871580000051
And
Figure BDA0003093871580000052
and time domain simulation results of the new energy grid-connected inverter.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
Fig. 1 is a schematic diagram of fault stage division of a new energy grid-connected inverter. Fig. 2 is a diagram illustrating a control structure of a typical pll.
The method comprises the following specific implementation steps:
A1) the new energy grid-connected inverter adopts a generator routine and utilizes a grid voltage d-axis orientation mode to acquire a grid-connected point three-phase voltage signal UtConverting the three-phase static coordinate system into a two-phase rotating coordinate system to obtain two-phase direct current quantity Utd、Utq；
A2) Will UtqAs an input signal of the phase-locked loop, the phase-locked loop output angular frequency ω is calculated according to the following formulaPLL：
ωPLL＝kppUtq+kip∫Utqdt+ωg
Wherein k isppAnd kipProportional and integral coefficients, omega, of the phase-locked loop, respectivelygIs the grid angular frequency rating;
A3) on the basis of the step A2), quantifying the transient stability margin of the new energy grid-connected inverter switched from the normal operation stage to the fault continuation stage according to the following formula:
Figure BDA0003093871580000053
wherein S isacc1、Sdec1And
Figure BDA0003093871580000057
respectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter switched from the normal operation stage to the fault continuation stage; delta d axis of phase-locked loop coordinate system and power grid voltage UgThe phase angle difference of (1), namely the equivalent power angle; delta0Is the equivalent power angle, delta, of the new energy grid-connected inverter at the initial moment of the fault detection stage1Is the equivalent power angle, delta, of the new energy grid-connected inverter at the initial moment of the fault duration stagemax1The upper limit value omega of the equivalent power angle of the new energy grid-connected inverter in the fault continuation stagebIs the angular frequency base value, UgfIs the voltage amplitude of the grid fault point, LgAnd RgRespectively the equivalent inductance and resistance of the point-to-point transmission line,
Figure BDA0003093871580000054
and
Figure BDA0003093871580000055
respectively an active current instruction and a reactive current instruction during low voltage ride through of the new energy grid-connected inverter, IdmFor the current limiting value, S, of the grid-side converter (GSC) of the new energy grid-connected inverternmThe transient stability margin evaluation value is used for switching the new energy grid-connected inverter from a normal operation stage to a fault continuation stage;
A4) according to the step A3), calculating the equivalent limit cut-off angle of the new energy grid-connected inverter according to the following formula
Figure BDA0003093871580000056
Figure BDA0003093871580000061
A5) Obtained according to step A4)
Figure BDA0003093871580000062
Calculating the fault detection limit time of the new energy grid-connected inverter according to the following formula, namely equivalent limit removal time
Figure BDA0003093871580000063
Figure BDA0003093871580000064
A6) The transient stability criterion for switching the new energy grid-connected inverter from the normal operation stage to the fault continuation stage is as follows:
Figure BDA0003093871580000065
wherein, tdelayDelays for actual fault detection; if tdelayThe stability criterion is not met, and the new energy grid-connected inverter generates a transient instability phenomenon;
A7) on the basis that the new energy grid-connected inverter meets the stability criterion obtained in the step A6), calculating the transient stability margin of the new energy grid-connected inverter in the fault continuation stage according to the following formula:
Figure BDA0003093871580000066
wherein S isacc2、Sdec2And
Figure BDA0003093871580000068
respectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter in the fault continuation stage; delta2Is a fault continuation phase omegaPLLAnd omegagWhen the equivalent power angle is equal, the equivalent power angle of the new energy grid-connected inverter is obtained; deltamin1To failLower limit value delta of equivalent power angle of new energy grid-connected inverter in continuous phasekAn equivalent power angle S corresponding to a balance working point of the new energy grid-connected inverter in the fault continuation stagedmThe value is the transient stability margin evaluation value S of the new energy grid-connected inverter in the fault continuation stagedmThe larger the system stability margin is, the higher the transient stability is;
A8) the transient stability criterion of the new energy grid-connected inverter in the fault continuation stage is as follows:
Figure BDA0003093871580000067
when the new energy grid-connected inverter meets the stability criterion, the new energy grid-connected inverter can smoothly reach and stably operate in a low-voltage ride-through control mode in a fault continuous stage;
A9) after the fault is cleared, the transient stability margin of the new energy grid-connected inverter switched from the fault continuous stage to the fault recovery stage can be quantified according to the following formula:
Figure BDA0003093871580000071
wherein S isacc3_4、Sdec4And
Figure BDA0003093871580000077
respectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter switched from the fault continuous stage to the fault recovery stage; delta4Is the equivalent initial power angle, delta, of the new energy grid-connected inverter in the fault recovery stageeIs the equivalent power angle, delta, corresponding to the balance working point of the new energy grid-connected inverter in the fault recovery stagemax2An upper limit value U of an equivalent power angle of the new energy grid-connected inverter at the fault recovery stagegnFor mains voltage rating, UtdnTo a grid point voltage UtThe d-axis component of the nominal value,
Figure BDA0003093871580000072
is the power command value of the fault recovery stage; srmThe value is a transient stability margin evaluation value S of switching the new energy grid-connected inverter from a fault continuous stage to a fault recovery stagermThe larger the transient stability margin of the new energy grid-connected inverter is, the smaller the instability risk is;
A10) the transient stability criterion for switching the new energy grid-connected inverter from the fault continuous stage to the fault recovery stage is as follows:
Figure BDA0003093871580000073
when the new energy grid-connected inverter meets the stability criterion, the new energy grid-connected inverter can be successfully recovered to a stable operation state after the fault is cleared.
Description of the effects of the invention:
the time domain simulation results of the new energy grid-connected inverter when the fault detection delay is 5ms and 10ms are respectively given by the working condition 1 and the working condition 2 in fig. 3. When the voltage level of the power grid falls to 0.3p.u., the voltage level is calculated
Figure BDA0003093871580000074
As shown in condition 1 of FIG. 3, if the fault detection delay is 5ms, that is, the time delay is set to be less than the threshold
Figure BDA0003093871580000075
The transient stability criterion of switching the new energy grid-connected inverter from the normal operation stage to the fault continuation stage is met, the new energy grid-connected inverter can smoothly complete the stable transition of switching the new energy grid-connected inverter from the normal operation stage to the fault continuation stage, and the new energy grid-connected inverter enters a low-voltage ride-through mode; when the fault detection delay is increased to 10ms, i.e.
Figure BDA0003093871580000076
In the meantime, the transient stability criterion that the new energy grid-connected inverter is switched from the normal operation stage to the fault continuation stage is not met, and as shown in the working condition 2 of fig. 3, the new energy grid-connected inverter generates a frequency-raising step-out instability phenomenon in the process of entering the low voltage ride through mode.
FIG. 4 shows the current commands respectively
Figure BDA0003093871580000081
And
Figure BDA0003093871580000082
and time domain simulation results of the new energy grid-connected inverter. When the voltage level of the power grid drops to 0.3p.u., a current instruction
Figure BDA0003093871580000083
Figure BDA0003093871580000084
Then, S is obtained by calculationdm＝0.0312>0, meeting the transient stability criterion of the new energy grid-connected inverter in the fault continuation stage, as shown in the working condition 3 of fig. 4, the new energy grid-connected inverter can smoothly complete low voltage ride through in the fault continuation stage, and transient stable operation is realized; when the current is instructed
Figure BDA0003093871580000085
Then, S is obtained by calculationdm＝-0.8886<And 0, the transient stability criterion of the new energy grid-connected inverter in the fault continuation stage is not met, as shown in the working condition 4 of fig. 4, the new energy grid-connected inverter generates the phenomena of frequency reduction, step loss and instability in the fault continuation stage, and the low-voltage ride-through fails.
FIG. 5 shows that the power commands are respectively
Figure BDA0003093871580000086
And
Figure BDA0003093871580000087
and time domain simulation results of the new energy grid-connected inverter. When the voltage level of the power grid drops to 0.3p.u., a power instruction
Figure BDA0003093871580000088
Then, S is obtained by calculationrm＝0.1765>0, meeting the requirement of switching the new energy grid-connected inverter from the fault continuous stageAs shown in the working condition 5 of fig. 5, the transient stability criterion at the fault recovery stage is that the new energy grid-connected inverter can be successfully recovered to a stable operation state after the fault is cleared; when power command
Figure BDA0003093871580000089
Then, S is obtained by calculationrm＝-0.3907<And 0, the transient stability criterion of switching the new energy grid-connected inverter from the fault continuation stage to the fault recovery stage is not met, and as shown in the working condition 6 of fig. 5, the wind power grid-connected system has the frequency-increasing step-out instability phenomenon in the power recovery process and cannot be recovered to the rated operation state.
The method can judge whether the new energy grid-connected inverter has transient instability in different fault stages according to the grid voltage drop degree, controller delay, converter capacity limit of the new energy grid-connected inverter, active and reactive current instructions of the new energy grid-connected inverter in the fault continuation stage, power instructions of the new energy grid-connected inverter in the fault recovery stage, phase-locked loop parameters and transmission line impedance, and quantitatively calculate the transient stability margin value of the new energy grid-connected inverter, so that a quantitative evaluation basis is provided for the transient synchronization stability of the new energy grid-connected inverter.
Finally, it should be noted that the above-mentioned examples of the present invention are only examples for illustrating the present invention, and are not intended to limit the embodiments of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it will be apparent to those skilled in the art that other variations and modifications can be made based on the above description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.

Claims (1)

1. A new energy grid-connected inverter transient stability margin evaluation method is used for judging the transient stability of the new energy grid-connected inverter in different fault stages, and is characterized in that: the method comprises the following specific steps:
A1) the new energy grid-connected inverter adopts a generator routine and utilizes a grid voltage d-axis orientation mode to acquire a grid-connected point three-phase voltage signal UtConverting the three-phase static coordinate system into a two-phase rotating coordinate system to obtain two-phase direct current quantity Utd、Utq；
A2) Will UtqAs an input signal of the phase-locked loop, the phase-locked loop output angular frequency ω is calculated according to the following formulaPLL：
ωPLL＝kppUtq+kip∫Utqdt+ωg
Wherein k isppAnd kipProportional and integral coefficients, omega, of the phase-locked loop, respectivelygIs the grid angular frequency rating;
A3) on the basis of the step A2), quantifying the transient stability margin of the new energy grid-connected inverter switched from the normal operation stage to the fault continuation stage according to the following formula:
Figure FDA0003093871570000011
wherein S isacc1、Sdec1And Δ EDⅠRespectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter switched from the normal operation stage to the fault continuation stage; delta d axis of phase-locked loop coordinate system and power grid voltage UgThe phase angle difference of (1), namely the equivalent power angle; delta0Is the equivalent power angle, delta, of the new energy grid-connected inverter at the initial moment of the fault detection stage1Is the equivalent power angle, delta, of the new energy grid-connected inverter at the initial moment of the fault duration stagemax1The upper limit value omega of the equivalent power angle of the new energy grid-connected inverter in the fault continuation stagebIs the angular frequency base value, UgfIs the voltage amplitude of the grid fault point, LgAnd RgRespectively the equivalent inductance and resistance of the point-to-point transmission line,
Figure FDA0003093871570000012
and
Figure FDA0003093871570000013
respectively an active current instruction and a reactive current instruction during low voltage ride through of the new energy grid-connected inverter, IdmFor the current amplitude limiting value S of the network side converter of the new energy grid-connected inverternmThe value is a transient stability margin evaluation value of switching the new energy grid-connected inverter from a normal operation stage to a fault continuation stage;
A4) according to the step A3), calculating the equivalent limit cut-off angle of the new energy grid-connected inverter according to the following formula
Figure FDA0003093871570000014
Figure FDA0003093871570000021
A5) Obtained according to step A4)
Figure FDA0003093871570000022
Calculating the fault detection limit time of the new energy grid-connected inverter according to the following formula, namely equivalent limit removal time
Figure FDA0003093871570000023
Figure FDA0003093871570000024
A6) The transient stability criterion for switching the new energy grid-connected inverter from the normal operation stage to the fault continuation stage is as follows:
Figure FDA0003093871570000025
wherein, tdelayIs a reality ofIf t, the fault detection ofdelayThe stability criterion is not met, and the new energy grid-connected inverter generates a transient instability phenomenon;
A7) on the basis that the new energy grid-connected inverter meets the stability criterion obtained in the step A6), calculating the transient stability margin of the new energy grid-connected inverter in the fault continuation stage according to the following formula:
Figure FDA0003093871570000026
wherein S isacc2、Sdec2And Δ EDⅡRespectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter in the fault continuation stage; delta2Is a fault continuation phase omegaPLLAnd omegagWhen the equivalent power angle is equal, the equivalent power angle of the new energy grid-connected inverter is obtained; deltamin1The lower limit value delta of the equivalent power angle of the new energy grid-connected inverter in the fault continuation stagekAn equivalent power angle S corresponding to a balance working point of the new energy grid-connected inverter in the fault continuation stagedmThe value is the transient stability margin evaluation value S of the new energy grid-connected inverter in the fault continuation stagedmThe larger the system stability margin is, the higher the transient stability is;
A8) the transient stability criterion of the new energy grid-connected inverter in the fault continuation stage is as follows:
Figure FDA0003093871570000027
when the new energy grid-connected inverter meets the stability criterion, the new energy grid-connected inverter can smoothly reach and stably operate in a low-voltage ride-through control mode in a fault continuous stage;
A9) after the fault is cleared, the transient stability margin of the new energy grid-connected inverter switched from the fault continuous stage to the fault recovery stage can be quantified according to the following formula:
Figure FDA0003093871570000031
wherein S isacc3_4、Sdec4And Δ EDⅢRespectively representing the equivalent acceleration area, the equivalent deceleration area and the equivalent energy consumption of the new energy grid-connected inverter switched from the fault continuous stage to the fault recovery stage; delta4Is the equivalent initial power angle, delta, of the new energy grid-connected inverter in the fault recovery stageeIs the equivalent power angle, delta, corresponding to the balance working point of the new energy grid-connected inverter in the fault recovery stagemax2An upper limit value U of an equivalent power angle of the new energy grid-connected inverter at the fault recovery stagegnFor mains voltage rating, UtdnTo a grid point voltage UtThe d-axis component of the nominal value,
Figure FDA0003093871570000032
is the power command value of the fault recovery stage; srmThe value is a transient stability margin evaluation value S of switching the new energy grid-connected inverter from a fault continuous stage to a fault recovery stagermThe larger the transient stability margin of the new energy grid-connected inverter is, the smaller the instability risk is;
A10) the transient stability criterion for switching the new energy grid-connected inverter from the fault continuous stage to the fault recovery stage is as follows:
Figure FDA0003093871570000033
when the new energy grid-connected inverter meets the stability criterion, the new energy grid-connected inverter can be successfully recovered to a stable operation state after the fault is cleared.
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