CN114784868A - Parameter stability boundary-based virtual impedance design method for network-following type inverter - Google Patents

Parameter stability boundary-based virtual impedance design method for network-following type inverter Download PDF

Info

Publication number
CN114784868A
CN114784868A CN202210510323.XA CN202210510323A CN114784868A CN 114784868 A CN114784868 A CN 114784868A CN 202210510323 A CN202210510323 A CN 202210510323A CN 114784868 A CN114784868 A CN 114784868A
Authority
CN
China
Prior art keywords
impedance
var
following
power grid
inverter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202210510323.XA
Other languages
Chinese (zh)
Inventor
甘德刚
苟家波
胡宇飞
李胜
戴炜
杨勇波
田震
查晓明
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Panzhihua Power Supply Co Of State Grid Sichuan Electric Power Corp
Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd
Original Assignee
Panzhihua Power Supply Co Of State Grid Sichuan Electric Power Corp
Wuhan University WHU
Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Panzhihua Power Supply Co Of State Grid Sichuan Electric Power Corp, Wuhan University WHU, Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd filed Critical Panzhihua Power Supply Co Of State Grid Sichuan Electric Power Corp
Priority to CN202210510323.XA priority Critical patent/CN114784868A/en
Publication of CN114784868A publication Critical patent/CN114784868A/en
Pending legal-status Critical Current

Links

Images

Classifications

    • 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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2113/00—Details relating to the application field
    • G06F2113/04—Power grid distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • 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

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Evolutionary Computation (AREA)
  • Geometry (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a parameter stability boundary-based virtual impedance design method for a net-following type inverter, which comprises the following steps of: step 1: analyzing system parameters of a power grid system formed by a grid-following inverter to obtain initial values, actual values and stability boundary values of the system parameters influencing the stability of the power grid system; step 2: calculating a virtual impedance R introduced into the network-following inverter according to the initial value, the actual value and the stable boundary value of each system parameterv. The method disclosed by the invention carries out quantitative calculation on the impedance value of the accessed impedance based on the parameter stable boundary, and the calculation step is simpler and more convenient; system equivalent resistance determination using system parameter stability and instability boundariesThe impedance value of the impedance is determined, and the system parameter which has larger influence on the stability of the system is selected as the basis for calculating the impedance value, so that the required impedance value can be calculated quantitatively, and the result is more accurate.

Description

Parameter stability boundary-based virtual impedance design method for network-following type inverter
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a method for designing virtual impedance of a network-following inverter based on a parameter stable boundary.
Background
With the rapid development of renewable energy sources such as wind power and photovoltaic, the permeability of a power electronic converter serving as an important interface for new energy grid connection in a power system is continuously improved, and the development of a modern power system gradually shows a trend of 'double high'.
Most of new energy grid-connected inverters are grid-following inverters, the external characteristics of the new energy grid-connected inverters are represented by current sources, the high-efficiency utilization of distributed power sources is realized by directly controlling output current, and the new energy grid-connected inverters lack frequency and voltage supporting capacity. In a 100% new energy island microgrid system which takes a power electronic converter as a leading factor, due to the low inertia and weak damping characteristics of the system and the lack of stable frequency and voltage support of a large power grid, when system parameters are set improperly, a phase-locked loop of a grid-following inverter may be unstable due to the lack of damping, so that the grid-following inverter cannot keep synchronization with a grid-forming inverter, and finally, the island microgrid system cannot keep stable operation.
Disclosure of Invention
The invention aims to provide a method for designing virtual impedance of a net-following type inverter based on a parameter stable boundary, which can quantitatively design the virtual impedance and has more accurate result. Virtual impedance is introduced into the grid-following type inverter so as to effectively avoid the situation that the grid-following type inverter is unstable due to lack of damping caused by improper setting of parameters of a power grid system.
Therefore, the invention provides a method for designing the virtual impedance of the net-following type inverter based on the parameter stable boundary, which comprises the following steps:
step 1: analyzing system parameters of a power grid system formed by a grid-following inverter to obtain initial values, actual values and stability boundary values of the system parameters influencing the stability of the power grid system;
and 2, step: calculating a virtual impedance R introduced into the network-following inverter from the initial values, the actual values and the stability boundary values of the system parametersvThe calculation formula is as follows:
Figure BDA0003637490860000021
in the formula, var1N,......,varnNSystem parameters var influencing system stability in power grid system formed by network-following inverters1,......,varnAn initial value of (1); var1s,......,varnsRespectively are each system parameter var1,......,varnActual value of (a); var1max,......,varnmaxRespectively are each system parameter var1,......,varnStability limit value, k, for stabilizing the systemvIs a virtual impedance constant.
The invention provides another scheme of a design method of virtual impedance of a network-following inverter based on a parameter stable boundary, which comprises the following steps: the method is used for the virtual impedance R of the inverter introduced into the network following typevDesign is performed, the virtual impedance RvFor varying the output of the net-following inverter; what is needed isThe network following type inverter is used for constructing a power grid system, and the constructed power grid system comprises a network construction type inverter, a network following type inverter and a connecting line; establishing a sequence impedance model of a network-constructing inverter, a network-following inverter, an inverter tie line impedance and a constant load in the constructed power grid system to obtain a Nyquist stability criterion, and calculating a stability boundary value of each system parameter and a system equivalent resistance of an instability boundary as a virtual impedance RvA designed step 1; virtual impedance R is calculated based on the stable boundary of each system parameter and the system equivalent resistance of the unstable boundaryvAs a virtual impedance RvStep 2 of designing.
In another aspect of the invention herein, a network-following inverter is provided, which is connected to a virtual impedance RvThe virtual impedance RvThe method is designed by the virtual impedance design method of the net-following type inverter based on the parameter stable boundary.
The invention provides an island micro-grid system, which comprises the grid-following type inverter.
By adopting the technical scheme of the invention, the technical effects at least comprise that:
1) the design method provided by the technical scheme performs quantitative calculation on the impedance value of the accessed impedance based on the parameter stability boundary, and the calculation steps are simpler and more convenient.
2) The technical scheme is based on the sequence impedance model, and the stability of the system is analyzed by adopting Nyquist stability criterion, so that the method has the advantages of simple and convenient calculation steps and concise calculation results; (other stability analysis methods such as generalized Nyquist stability criterion based on dq impedance model, characteristic value analysis based on state space model, etc. all the calculation process is more complicated);
3) according to the technical scheme, the impedance value of the impedance is determined by using the system equivalent resistance of the system parameter stable boundary and the system equivalent resistance of the unstable boundary, and the system parameter which has a large influence on the system stability is selected as the basis for calculating the impedance value, so that the required impedance value can be calculated quantitatively, and the result is more accurate.
4) The technical scheme introduces impedance into the inverter, the impedance value of the impedance is determined by the values of all system parameters influencing the stability of a power grid system formed by the grid-following inverter, certain self-adaptation is realized, the damping of the grid-following inverter is improved, and the condition that the grid-following inverter is unstable due to lack of damping caused by improper setting of the parameters of the power grid system is effectively avoided.
5) When the grid-following type inverter is constructed into a power grid system, the condition that the grid-following type inverter is unstable due to lack of damping caused by improper setting of parameters of the power grid system can be effectively avoided, the influence of the output of the grid-following type inverter on the stable working point of the power grid system is reduced, the damping of the power grid system is equivalently improved, and the stability of the power grid system is improved to a certain extent.
6) Impedance is installed in following the control circuit of net type dc-to-ac converter among this technical scheme, and the impedance of introducing belongs to secondary equipment, has avoided modifying the electric wire netting system, has the installation and overhauls the convenience, equipment requirement and advantage such as cost are lower.
7) The impedance is installed in the control circuit of following net type dc-to-ac converter among this technical scheme, easily operates, and the cost is lower relatively.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:
fig. 1 is a circuit topology diagram of a control loop of a network-following inverter disclosed by the invention;
FIG. 2 is a main circuit topology diagram of the grid system disclosed by the present invention;
FIG. 3 is a diagram of an equivalent impedance network model according to the present disclosure;
FIG. 4 is a comparison of the stability enhancement effect of the present invention.
PCC in the figure denotes a point of grid connection.
Detailed Description
Exemplary embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. In the drawings, the size of some of the elements may be exaggerated or distorted for clarity. The same reference numerals denote the same or similar structures in the drawings, and thus detailed descriptions thereof will be omitted.
In order to effectively avoid the situation that the grid-following inverter lacks damping instability due to improper parameter setting of a power grid system, the virtual impedance R is introduced into the grid-following invertervTo change the output of the network-following inverter; the impedance RvThe impedance value of (a) is determined by the values of the system parameters affecting the stability of the grid system formed by the grid-following inverter.
In this disclosure, the virtual impedance RvIs introduced into a control loop of a grid-follower inverter circuit, the control loop circuit topology being exemplarily shown in fig. 1, including:
a q-axis branch configured to include a first operator, a first PI regulator for non-static tracking of DC component in synchronous coordinate system, a second operator, and a first K for dq decoupling controldpA module;
a d-axis branch configured to include a third operator, a second PI regulator for non-static tracking of DC component in synchronous coordinate system, a fourth operator, and a second K for dq decoupling controldpA module; and
and the coordinate transformation module dq/abc is used for converting the input signal from a dq coordinate system to an abc coordinate system.
q-axis reference current IqrefQ-axis current component I in synchronous rotating coordinate system with grid connection pointqRespectively introducing a first arithmetic unit, a second arithmetic unit and a first K via a first PI regulatordpThe signal output by the module is introduced into a second arithmetic unit; d-axis reference current IdrefIn synchronous rotation with the point of connectionD-axis current component I of coordinate systemdRespectively introducing a third arithmetic unit, a fourth arithmetic unit and a second K through a second PI regulatordpThe signal output by the module is introduced into a fourth arithmetic unit; the outputs of the second arithmetic unit and the fourth arithmetic unit are respectively introduced into a coordinate transformation module dq/abc to output a modulation wave eabc。
The inverter is introduced with a virtual impedance RvTo change the output of the grid-following inverter, the coordinate transformation module dq/abc outputs a modulation wave eabcIntroducing a fifth operator and ioabc RvComputing to obtain a through impedance RvObtaining the final modulated wave
Figure BDA0003637490860000051
Is switched into the impedance RvThe rear-output modulation wave becomes:
Figure BDA0003637490860000052
eabcis not connected to the virtual impedance RvModulating waves by a network-following inverter;
Figure BDA0003637490860000053
for accessing a virtual impedance RvModulating waves by a network-following inverter; i all right angleoabcThe three-phase output current of the net-tracking type inverter.
In this disclosure, the virtual impedance RvObtained by the following expression:
Figure BDA0003637490860000054
in the formula, var1N,......,varnNSystem parameters var influencing system stability in power grid system formed by network-following inverters1,......,varnThe initial value of (1); var (var)1s,......,varnsRespectively are each system parameter var1,......,varnActual value of (a); var1max,......,varnmaxRespectively are each system parameter var1,......,varnStability limit value, k, for stabilizing the systemvIs a virtual impedance constant. Wherein each system parameter var1,......,varnIs the initial value of each system parameter that can keep the system operating stably.
Virtual impedance R for ensuring accessvThe power grid system can not be destabilized, and the virtual impedance constant is ensured to be R when taking valuesvThe impedance value of (a) satisfies:
Figure BDA0003637490860000055
in the formula: r iseq1,......,ReqnFor each system parameter var1,......,varnThe equivalent loop resistances of the power grid system at the moment of power grid system instability are respectively Req1,......,Reqn＝Re[Zeq1],......,Re[Zeqn]；Zeq1.....ZeqnRespectively obtaining through the following expressions:
Zeq＝Zload+(Z11+Zg11)//......//(Z1i+Zg1i)//(Z21+Zg21)//......//(Z2j+Zg2j)
in the formula: zloadSequence resistance for constant load of power grid system, (Z)11+Zg11)//......//(Z1i+Zg1i) Parallel impedance of i network-forming inverter branches for constructing a power grid system; (Z)21+Zg21)//......//(Z2j+Zg2j) Parallel impedance of j following net type inverter branches of a power grid system is constructed.
The main circuit topology of the power grid system constructed by the network following type inverter comprises i network construction type inverter branches, j network following type inverter branches, inverter tie line impedance and constant load sequence impedance, and is shown in figure 2. The virtual impedance R is calculated according to the power grid system and by combining the following stepsvThe impedance values of (a) are described in more detail.
Step 1: establishing a network-constructing inverter, a network-following inverter, inverter tie line impedance and a sequence impedance model of a constant load in the constructed power grid system to obtain a Nyquist stability criterion, and calculating a stability boundary value of each system parameter and a system equivalent resistance of an instability boundary; specifically, the step includes the following substeps:
step 1.1: establishing a sequence impedance model Z of i network-constructing inverters forming a power grid system11,......,Z1i(ii) a Sequence impedance model Z of j-table net-following type inverter21,......,Z2jSequence impedance model Z of interconnection line of grid-forming type inverterg11,......,Zg1iSequence impedance model Z of tie line of grid-following type inverterg21,......Zg2jAnd a constant-load sequence impedance model Zload；
Step 1.2: based on the sequence impedance model in step 1.1, an equivalent impedance network model of the power grid system is established, as shown in fig. 3, and accordingly, an expression of output current of a grid-connected point is obtained as follows:
Figure BDA0003637490860000061
Figure BDA0003637490860000062
when H is present11(s),......,H1k(s) when no positive real part pole exists, the stability of the power grid system depends on H21(s),......,H2l(s) and H3(s)，H21(s),......,H2l(s) and H3(s) can be regarded as a closed loop transfer function, the stability of which depends on the open loop transfer function Lm1(s),......,Lml(s) and Lm(s) when Lm1(s),......,Lml(s) and Lm(s) when the Nyquist stability criterion is met, the power grid system is stable, and accordingly, initial system parameters influencing the stability of the power grid system are obtained, such as: inverter tie line inductance LgiD-axis output current reference value I of grid-following inverterdrefiConstant load impedance ZloadEtc.;
step 1.3: modifying step 1.2 to obtain each initial system parameter (such as inductance L of inverter tie line)giD-axis output current reference value I of grid-following inverterdrefiConstant load impedance ZloadEtc.), the stability of the power grid system under different parameter values is judged according to a Nyquist stability criterion, and various system parameters which have great influence on the stability of the power grid system are found out and respectively marked as: var (var)1,......,varn(ii) a And determining limit values of all system parameters to enable the power grid system to keep stable as stable boundary values, wherein the limit values are marked as follows: var (var)1max,......,varnmax(ii) a The stability margin may be found based on the system stability analysis results;
step 1.4: calculating the equivalent loop impedance Z under the stable boundary value of each system parametereqEquivalent loop impedance ZeqThe real part of the resistance is equivalent loop resistance R of the power grid system at the moment that the power grid system is unstable due to each system parametereq(ii) a The stable boundary is a limit at which the power grid system is stable, and is also a boundary at which the power grid system is unstable, that is, when a certain parameter affecting the system is configured to a certain parameter value, the value keeps the power grid system stable, and when the parameter value is exceeded, the system is unstable, and the set parameter value is a boundary value which ensures the system to be stable, and is also a boundary value at which the system is unstable.
In the present disclosure, the condition that the system parameter determined as the system parameter having a large influence on the stability of the power grid system satisfies is: a stably operating system should be attributed a parameter that has a greater impact on system stability when it is unstable due to an improper setting (or modification) of the parameter.
Wherein, the equivalent loop impedance Z under each system parametereqCalculated by the following expression:
Zeq＝Zload+(Z11+Zg11)//......//(Z1i+Zg1i)//(Z21+Zg21)//......//(Z2j+Zg2j)
in the formula: z is a linear or branched memberloadSequence resistance for constant load of power grid system, (Z)11+Zg11)//......//(Z1i+Zg1i) The impedance is the parallel impedance of i network-forming inverter branches; (Z)21+Zg21)//......//(Z2j+Zg2j) The parallel impedances of j network following type inverter branches are obtained.
Such as calculating a stable boundary value var at the kth critical system parameterkmaxSequence impedance Z of lower network-building type inverter11k,......,Z1ikSequence impedance Z of and net-following type inverter21k,......,Z2jkAnd corresponding tie line sequence impedance Zg11k,......,Zg1ikAnd Zg21k,......Zg2jkAt this time, the equivalent loop impedance of the system is ZeqkThe calculation formula is as follows:
Zeqk＝Zload+(Z11k+Zg11k)//......//(Z1ik+Zg1ik)//(Z21k+Zg21k)//......//(Z2jk+Zg2jk) (ii) a Corresponding system equivalent resistance is Reqk＝Re[Zeqk]I.e. the system equivalent loop impedance ZeqkThe real part of (a).
And 2, step: virtual impedance R is calculated based on the stable boundary of each system parameter and the system equivalent resistance of the unstable boundaryvThe step is embodied in calculating the virtual impedance R by using the following expressionv：
Figure BDA0003637490860000081
In the formula, var1N,......,varnNRespectively setting the initial values of the system parameters; var (var)1s,......,varnsRespectively taking actual values of each system parameter; k is a radical of formulavIs a virtual impedance constant.
Wherein the virtual impedance constant kvIs chosen such that the virtual impedance R isvSatisfies the following conditions:
Figure BDA0003637490860000082
in a 100% new energy island microgrid system taking a power electronic converter as a leading factor, due to the low inertia and weak damping characteristics of the microgrid system and the lack of stable frequency and voltage support of a large power grid, when system parameters are improperly set, a tracking grid type inverter phase-locked loop may be unstable due to the lack of damping, so that the island microgrid system cannot keep stable operation.
Therefore, the invention provides the network following type inverter, the virtual impedance is introduced into a control loop of the inverter, the virtual impedance is designed by the value of each system parameter influencing the stability of a power grid system formed by the network following type inverter, certain self-adaptation is realized, the damping of the network following type inverter is improved, and the condition that the network following type inverter is lack of damping instability due to improper setting of the power grid system parameters is effectively avoided. With this disclosed with net type dc-to-ac converter constitute island little grid system or other grid system, can reduce because of the influence of grid system parameter setting improper and leading to with net type dc-to-ac converter to island little grid system steady state operating point because of lacking the damping, strengthened the little grid system stability of island.
The main circuit topological structure of an island micro-grid system constructed by the grid-following type inverter is shown in fig. 2, and the determination of the impedance value of virtual impedance introduced by the grid-following type inverter in the island micro-grid system is described by taking 1 grid-forming type inverter and 1 grid-following type inverter as examples. It should be understood by those skilled in the art that 1 stage is taken as an example for illustration, and only 1 stage is not shown, but can be configured as i stage and j stage respectively.
The impedance value of virtual impedance introduced by a grid-following inverter in an island micro-grid system is determined by the following steps:
step 1: establishing sequence impedance model Z of 1 network-constructing inverter11Sequence admittance model Z of 1 following net type inverter21Sequence impedance model Z of interconnection line of grid-forming type inverterg11Sequence impedance model Z of net-following type inverter connecting lineg21And a constant-load sequence impedance model Zload；
Step 2: establishing an equivalent impedance network model of the island microgrid system based on the sequence impedance model in the step 1, wherein as shown in fig. 3, the output current expression of a grid-connected point is
IPCC＝(H11·Vs1+H21·Is1)·H3
Figure BDA0003637490860000091
When H is present11When no positive real part pole exists in(s), the stability of the island micro-grid system depends on H21(s) and H3(s)。H21(s) and H3(s) can be regarded as a closed loop transfer function, the stability of which depends on the open loop transfer function Lm1(s) and Lm(s). Therefore, when L ism1(s) and LmAnd(s) when the Nyquist stability criterion is met, the isolated island micro-grid system is stable.
And 3, step 3: modifying the parameter values of the initial system parameters obtained in the step 1.2, judging the stability of the power grid system under different parameter values according to a Nyquist stability criterion, and finding out the system parameters which have larger influence on the system stability and are respectively the inductance L of the network-following inverterg21And d-axis output current reference value I thereofdref1Meanwhile, based on the system stability analysis result, the stability boundary values of all the parameters are found out to be L respectivelyg21max＝5mH、Id1max＝20A。
And 4, step 4: calculating stable limit values L of different system parametersg21max、Id1maxThe equivalent loop impedances of the lower systems are respectively Zeq1、Zeq2The corresponding system equivalent resistance is Req1＝Re[Zeq1]、Req2＝Re[Zeq2]；
And 5: stability margin L based on parametersg21max、Id1maxAnd system equivalent resistance R of instability boundaryeq1、Req2Designing the impedance of the grid-following inverter to be
Figure BDA0003637490860000101
In the formula, Lg21N、Idref1NAre respectively Lg21、Idref1An initial value of (1); l isg21s、Id1sRespectively, the system parameter Lg21、Idref1Actual value of (2); k is a radical ofvIs a virtual impedance constant, which is taken to be such that the virtual impedance satisfies:
Figure BDA0003637490860000102
determining the virtual impedance R by the above stepsvAfter impedance value is introduced into a control loop of the grid-connected inverter, as shown in fig. 1, the modulation wave of the grid-connected inverter is changed into:
Figure BDA0003637490860000103
eabcis not connected to the impedance RvModulating waves by a network-following inverter;
Figure BDA0003637490860000104
to access an impedance RvModulating waves by a network-following inverter; i all right angleoabcThe three-phase output current of the net-tracking type inverter.
Changing the virtual impedance constant to make the virtual impedance RvIn contrast, as shown in FIG. 4, the constant coefficients k are different virtual impedancesvAnd changing a simulation waveform comparison diagram of the islanding micro-grid system when the d-axis output current reference value of the grid-following inverter is changed. In the figure, δ2Is the phase angle difference of local dq coordinate axes of the grid-forming inverter and the grid-following inverter (taking the grid-following inverter as a reference), f is the output frequency of a phase-locked loop of the grid-following inverter, Id is the output current of a d axis of the grid-following inverter, and a solid line is kvSimulated waveform of 0.5, with k as the dotted linevThe simulated waveform is 0.1. Increasing d-axis output current reference value I of grid-following type inverterdref1Increasing it from 14A to a stable boundary 20A. Comparing different virtual impedance constant coefficients kvThe lower simulation waveform shows kvThe larger the impedance RvThe larger, the stability to the systemThe better the lifting effect. When k isvWhen equal to 0.1, due to the impedance Rv＜max{|Req1|,|Req2L, resulting in a reference value I of the output current of the d-axis of the grid-following inverterdref1Reach a stable boundary Id1maxWhen the voltage is 20A, sufficient damping support cannot be provided for the system, and instability of the islanded microgrid system is finally caused. When k isvWhen the damping value is equal to 0.5, the system is supported by enough damping, the simulation waveform of the system tends to be stable after small-amplitude damping oscillation, and the system can keep stable operation.
In the present disclosure, the grid-connected inverter is a grid-connected inverter based on VSG control, and the grid-connected inverter is a current-controlled grid-connected inverter, and the grid-connected inverter and the current-controlled grid-connected inverter are configured to include: DC power supply (V)dc11......Vdc1i、Vdc21......Vdc2i) Converter VSC for converting direct current into alternating current and providing grid-connected current and grid-connected point voltage, and filter inductor (L)f11......Lf1i/Lf21......Lf2i) Inverter impedance (R)f11......Rf1i/Rf21......Rf2i) Filter capacitor (C)f11......Cf1i/Cf21......Cf2i). The constructed power grid is also configured to include a tie line impedance (R)g11......Rg1i/Rg11......Rg2i) An interconnection line inductance (L)g11......Lg1i/Lg21......Lg2i) And a constant load impedance Zload。
Of course, other types of configurations of the network formation type and the network tracking type are also possible.
Virtual impedance R of the present disclosurevIs introduced into the following network type inverter in an independent mode, and avoids primary equipment (not connected with an impedance R) of a power grid systemvThe power grid structure and the grid-following type inverter) and has the advantages of convenient installation and maintenance, lower equipment requirement and cost and the like.
It should be understood that parts of the specification not set forth in detail are well within the prior art. Although specific embodiments of the present invention have been described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that these are merely illustrative and that various changes or modifications may be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is only limited by the appended claims.

Claims (10)

1. A method for designing virtual impedance of a net-following type inverter based on a parameter stable boundary is characterized by comprising the following steps:
step 1: analyzing system parameters of a power grid system formed by a grid-following inverter to obtain initial values, actual values and stability boundary values of the system parameters influencing the stability of the power grid system;
and 2, step: calculating a virtual impedance R introduced into the network-following inverter from the initial values, the actual values and the stability boundary values of the system parametersvThe calculation formula is as follows:
Figure FDA0003637490850000011
in the formula, var1N,......,varnNSystem parameters var influencing system stability in power grid system formed by grid-following inverters1,......,varnThe initial value of (1); var1s,......,varnsAre respectively the system parameters var1,......,varnActual value of (2); var1max,......,varnmaxRespectively are each system parameter var1,......,varnStability limit value, k, for stabilizing the systemvIs a virtual impedance constant.
2. The design method of the virtual impedance of the net-following type inverter based on the parameter stable boundary is characterized in that: the virtual impedance constant kvIs such that the virtual impedance R isvSatisfies the following conditions:
Figure FDA0003637490850000012
in the formula: r iseq1,......,ReqnFor each system parameter var1,......,varnThe equivalent loop resistances of the power grid system at the moment of instability of the power grid system are respectively Req1,......,Reqn＝Re[Zeq1],......,Re[Zeqn]；Zeq1.....ZeqnRespectively obtaining through the following expressions: zeq＝Zload+(Z11+Zg11)//......//(Z1+Zg1i)//(Z21+Zg21)//......//(Z2+Zg2j) In the formula: zloadIs the sequence resistance of the constant load of the power grid system, (Z)11+Zg11)//......//(Z1+Zg1i) Parallel impedance of i network-forming inverter branches for constructing a power grid system; (Z)21+Zg21)//......//(Z2+Zg2j) The parallel impedance of j network-following type inverter branches of a power grid system is constructed.
3. The method for designing the virtual impedance of the net-tracking inverter based on the parameter stability boundary according to claim 1, wherein each system parameter var1,......,varnThe method is determined by the following steps:
step 1.1: establishing sequence impedance model Z of i-station network-forming type inverter forming power grid system11,......,Z1i(ii) a Sequence impedance model Z of j following net type inverter21,......,Z2jSequence impedance model Z of interconnection line of grid-forming type inverterg11,......,Zg1iSequence impedance model Z of net-following type inverter connecting lineg21,......Zg2jAnd a constant-load sequence impedance model Zload；
Step 1.2: based on the sequence impedance model in the step 1.1, an equivalent impedance network model of the power grid system is established, and output current of a grid connection point is established:
Figure FDA0003637490850000021
Figure FDA0003637490850000022
when L ism1(s),......,Lml(s) and Lm(s) when Nyquist stability criterion is met, stabilizing the power grid system, and accordingly obtaining initial system parameters influencing the stability of the power grid system;
step 1.3: modifying the step 1.2 to obtain each initial system parameter value, judging the stability of the power grid system under different parameter values according to a Nyquist stability criterion, obtaining each system parameter which has a large influence on the stability of the power grid system, and respectively marking as: var1,......,varn；
The stability limit value var1max,......,varnmaxAnd finding out each parameter based on the power grid system stability analysis result to ensure that the stability boundary of the system meeting the Nyquist stability criterion is determined as var1max,......,varnmax。
4. A method for designing virtual impedance of a net-following type inverter based on a parameter stable boundary is characterized by comprising the following steps: the method is used for virtual impedance R of an inverter introduced into a network following typevDesign is performed, the virtual impedance RvFor varying the output of the net-following inverter; the network following type inverter is used for constructing a power grid system, and the constructed power grid system comprises a network construction type inverter, a network following type inverter and a connecting line; establishing a sequence impedance model of the network-constructing inverter, the network-following inverter, the inverter tie line impedance and the constant load in the constructed power grid system to obtain a Nyquist stability criterion, and calculating a stability boundary value of each system parameter and a system equivalent resistance of an instability boundary as a virtual impedance RvA designed step 1; virtual impedance R is calculated based on the stable boundary of each system parameter and the system equivalent resistance of the unstable boundaryvAs a virtual impedance RvStep 2 of designing.
5. The design method of the virtual impedance of the net-following type inverter based on the parameter stable boundary is characterized in that: the 1 st process includes the following substeps:
step 1.1: establishing sequence impedance model Z of i-station network-forming type inverter forming power grid system11,......,Z1i(ii) a Sequence impedance model Z of j following net type inverter21,......,Z2jSequence impedance model Z of grid-structured inverter connecting lineg11,......,Zg1iSequence impedance model Z of tie line of grid-following type inverterg21,......Zg2jAnd a constant-load sequence impedance model Zload；
Step 1.2: based on the sequence impedance model in the step 1.1, an equivalent impedance network model of the power grid system is established, and accordingly, an output current expression of a grid-connected point is obtained as follows:
Figure FDA0003637490850000031
Figure FDA0003637490850000032
when L ism1(s),......,Lml(s) and Lm(s) when Nyquist criterion is met, the power grid system is stable, and initial system parameters influencing the stability of the power grid system are obtained;
step 1.3: modifying the step 1.2 to obtain each initial system parameter value, judging the stability of the power grid system under different parameter values according to a Nyquist stability criterion, obtaining each system parameter which has a large influence on the stability of the power grid system, and respectively marking as: var (var)1,......,varn(ii) a And acquiring system parameters to enable a power grid system to keep stable limit values as stable boundary values, and respectively marking as: var1max,......,varnmax；
Step 1.4: calculating the equivalent loop impedance Z of the power grid system under the stable boundary of each system parametereqThe equivalent loop impedance ZeqThe real part of the resistance is equivalent loop resistance R of the power grid system at the moment that the power grid system is unstable due to each system parametereq；
Equivalent loop impedance Z under each system parametereqCalculated by the following expression:
Zeq＝Zload+(Z11+Zg11)//......//(Z1i+Zg1i)//(Z21+Zg21)//......//(Z2j+Zg2j) In the formula: zloadSequence resistance for constant load of power grid system, (Z)11+Zg11)//......//(Z1i+Zg1i) The impedance is the parallel impedance of i network-forming inverter branches; (Z)21+Zg21)//......//(Z2j+Zg2j) The parallel impedances of the j following net type inverter branches are shown.
6. The design method of the virtual impedance of the net-following type inverter based on the parameter stable boundary is characterized in that: the 2 nd step calculates the virtual impedance R based on the stable boundary values of the respective system parameters by using the following expressionv，
Figure FDA0003637490850000041
In the formula, var1N,......,varnNRespectively setting initial values of system parameters; var (var)1s,......,varnsRespectively taking actual values of each system parameter; k is a radical ofvIs a virtual impedance constant; the virtual impedance constant kvIs chosen such that the virtual impedance R isvSatisfies the following conditions:
Figure FDA0003637490850000042
7. the method for designing the virtual impedance of the net-tracking inverter based on the parameter stability boundary according to claim 4, wherein the virtual impedance R isvIs connected into a control loop of the network-following type inverter.
8. The method for designing the virtual impedance of the grid-following inverter based on the parameter stability boundary according to claim 7, wherein the control loop comprises:
a q-axis branch configured to include a first operator, a first PI regulator for non-statics tracking of DC component in a synchronous coordinate system, a second operator, and a first KdpA module;
a d-axis branch configured to include a third operator, a second PI regulator for non-static tracking of DC component in synchronous coordinate system, a fourth operator, and a second KdpA module; and
a coordinate transformation module dq/abc;
q-axis reference current IqrefQ-axis current component I in synchronous rotating coordinate system with grid connection pointqRespectively introducing the first arithmetic unit and the second arithmetic unit through the first PI regulator, and introducing the first KdpThe signal output by the module is introduced into the second arithmetic unit;
d-axis reference current IdrefD-axis current component I in synchronous rotation coordinate system at point of grid connectiondRespectively introducing the third arithmetic unit and the fourth arithmetic unit and the second K through the second PI regulatordpThe signal output by the module is introduced into the fourth arithmetic unit;
the outputs of the second arithmetic unit and the fourth arithmetic unit are respectively led into the coordinate transformation module dq/abc to output a modulation wave eabcIntroducing a fifth operator and ioabc RvOperated to obtain the virtual impedance RvObtaining the final modulated wave
Figure FDA0003637490850000051
ioabcThe three-phase output current of the net-tracking type inverter.
9. The network following type inverter is characterized in that the network following type inverter is connected with a virtual impedance RvThe virtual impedance RvGrid-following inverter based on parameter stability boundary according to any one of claims 1 to 8And designing a virtual impedance design method.
10. An islanded microgrid system characterized in that it comprises a trawl-type inverter according to claim 9.
CN202210510323.XA 2022-05-11 2022-05-11 Parameter stability boundary-based virtual impedance design method for network-following type inverter Pending CN114784868A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202210510323.XA CN114784868A (en) 2022-05-11 2022-05-11 Parameter stability boundary-based virtual impedance design method for network-following type inverter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202210510323.XA CN114784868A (en) 2022-05-11 2022-05-11 Parameter stability boundary-based virtual impedance design method for network-following type inverter

Publications (1)

Publication Number Publication Date
CN114784868A true CN114784868A (en) 2022-07-22

Family

ID=82436103

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202210510323.XA Pending CN114784868A (en) 2022-05-11 2022-05-11 Parameter stability boundary-based virtual impedance design method for network-following type inverter

Country Status (1)

Country Link
CN (1) CN114784868A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117013594A (en) * 2023-06-26 2023-11-07 海南电网有限责任公司 Parameter setting method for current controller of micro-grid-connected inverter

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117013594A (en) * 2023-06-26 2023-11-07 海南电网有限责任公司 Parameter setting method for current controller of micro-grid-connected inverter

Similar Documents

Publication Publication Date Title
Song et al. Analysis of middle frequency resonance in DFIG system considering phase-locked loop
Shao et al. Power coupling analysis and improved decoupling control for the VSC connected to a weak AC grid
WO2018176599A1 (en) Mmc-based electromechanical transient simulation method and system for voltage source converter-based high voltage direct current and direct current power grid
WO2023083128A1 (en) Island microgrid system, and interactive oscillation suppression method and system therefor
Azab A finite control set model predictive control scheme for single-phase grid-connected inverters
CN111009921A (en) Double-fed fan grid-connected system oscillation analysis method based on Nyquist stability criterion
Babu et al. Investigation of damping effect of PLL on low-frequency harmonic stability of grid-tied inverter with αβ and dq current control schemes
CN114784868A (en) Parameter stability boundary-based virtual impedance design method for network-following type inverter
Yang et al. A broadband active damping method for high-frequency resonance suppression in MMC-HVDC system
CN112448407A (en) Impedance optimization control strategy for improving stability of grid-connected system under constant power control under bidirectional power flow
Xu et al. High-frequency resonance suppression based on unified MMC high-frequency impedance model
Liu et al. Impedance modeling and analysis of three-phase voltage-source converters viewing from DC side
Lin et al. Coordinated‐control strategy of scalable superconducting magnetic energy storage under an unbalanced voltage condition
Sun Power quality in renewable energy systems-Challenges and opportunities
Xue et al. Re-examination of small-signal instability in weak grid-connected voltage source converters
CN109347355A (en) The mathematical model and control method of nine switching mode gird-connected inverters
Wu et al. Multi-port admittance model and SISO stability criterion for oscillatory stability analysis of VSC-based AC/DC interconnected renewable systems
Li et al. An improved dual-loop feedforward control method for the enhancing stability of grid-connected PV and energy storage system under weak grids
CN113839413A (en) Parameter design method for inverter of alternating current-direct current hybrid power distribution network
Gao et al. Improved extended kalman filter based dynamic equivalent method of DFIG wind farm cluster
Zheng et al. DC-bus voltage damping characteristic analysis and optimization of grid-connected PMSG
Wang et al. DQ impedance modeling and stability analysis of virtual synchronous generator considering voltage current loop
CN112039113A (en) Impedance modeling method of NPC type three-phase three-level inverter
Pan et al. Enhanced grid forming control for MMC-HVDC with DC power and voltage regulation
Liu et al. Power Oscillation Analysis of PMSG Wind Power Generation System Considering Power Control Nonlinearity

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
TA01 Transfer of patent application right
TA01 Transfer of patent application right

Effective date of registration: 20230621

Address after: No. 5, Xinyuan Road, East District, Panzhihua City, Sichuan 610000

Applicant after: PANZHIHUA POWER SUPPLY COMPANY OF STATE GRID SICHUAN ELECTRIC POWER Corp.

Applicant after: STATE GRID SICHUAN ELECTRIC POWER Research Institute

Address before: No.5, Xinyuan Road, East District, Panzhihua City, Sichuan Province

Applicant before: PANZHIHUA POWER SUPPLY COMPANY OF STATE GRID SICHUAN ELECTRIC POWER Corp.

Applicant before: WUHAN University

Applicant before: STATE GRID SICHUAN ELECTRIC POWER Research Institute