CN114362167A - Method for evaluating transient voltage stability of power system - Google Patents

Method for evaluating transient voltage stability of power system Download PDF

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CN114362167A
CN114362167A CN202210033974.4A CN202210033974A CN114362167A CN 114362167 A CN114362167 A CN 114362167A CN 202210033974 A CN202210033974 A CN 202210033974A CN 114362167 A CN114362167 A CN 114362167A
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power system
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秦博宇
王明杰
张钢
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Northwest Branch Of State Grid Corp Of China
Xian Jiaotong University
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Xian Jiaotong 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • 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]

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Abstract

A method for evaluating transient voltage stability of a power system comprises the steps of establishing three-output power system scenes with different new energy permeabilities and three-output power system scenes with different direct current transmission capacities; calculating the input-output stability attribute of each subsystem in the three-output power system; calculating the stability criterion of the interconnected system according to the input-output stability attribute of the subsystem; and according to the stability criterion of the interconnected system, obtaining a quantitative evaluation index reflecting the voltage stability of the interconnected system, and evaluating the transient voltage stability of the power system and the transient voltage safety of the power system. According to the method, the system of different new energy permeability is constructed, and the stability of the system is quantized through the established indexes, so that the quantitative evaluation of the influence of the new energy permeability on the stability of the power grid can be realized. According to the invention, the transient voltage stability of the three-output system can be evaluated by constructing the three-output system with different direct current transmission capacities and quantifying the stability of the three-output system.

Description

Method for evaluating transient voltage stability of power system
Technical Field
The invention belongs to the technical field of new energy power generation, and relates to an evaluation method for transient voltage stability of a power system.
Background
The dynamic characteristics of the new energy generator set are obviously different from those of the traditional synchronous generator set, and the operation characteristics of a power grid are greatly changed along with the gradual improvement of the proportion of new energy grid connection, so that the analysis of the stability characteristic mechanism of the power grid is more complicated. And the distribution pattern of new energy resources such as wind energy, solar energy and the like and load centers in China determines that the transmission of new energy electric power must be realized through high-voltage direct-current transmission. When faults such as direct current locking, commutation failure and the like occur in the high-voltage direct current transmission system, severe transient voltage changes can be caused by large-amplitude reactive power fluctuation between a converter station and a power grid. The rapid development of new energy power generation and direct current transmission enables a power grid at a sending side to have the characteristics of high new energy permeability and large quantity of direct current sent out, and a multi-sending-out power system containing high proportion of new energy is gradually formed, which brings a serious challenge to the stability of the power grid at the sending side, so that a method capable of evaluating the coupling relation among the new energy permeability, the transmission capacity of a high-voltage direct current system and the transient voltage stability is urgently needed.
At present, the research methods for transient voltage stability of the power system mainly include an extended equal-area method, a transient function energy method, a time domain simulation method and the like. In the prior art, the influence of the new energy permeability and the direct current system transmission capacity on the voltage transient is mostly considered separately for the analysis of the transient voltage stability of the system, and the analysis of the coupling relationship among the new energy permeability, the direct current transmission capacity and the transient voltage stability is lacked. With the rapid development of the high-voltage direct-current system, a plurality of direct-current outgoing channels exist in the direct-current outgoing system, and the analysis of the transient voltage stability of the system by the plurality of outgoing direct currents is still fuzzy in the prior art. The multi-output power system containing a high proportion of new energy may be in an unsafe operation state and a fault state after suffering from interference, and how to evaluate the fault state boundary of the multi-output power system containing a high proportion of new energy after suffering from interference is also an important target of transient voltage stability analysis.
Disclosure of Invention
The invention aims to provide an evaluation method of transient voltage stability of a power system, which is used for solving the problem of evaluating the transient voltage stability of a multi-output power system containing high-proportion new energy.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for evaluating transient voltage stability of a power system comprises the following steps:
the method comprises the following steps: establishing three-output power system scenes with different new energy permeabilities and three-output power system scenes with different direct current transmission capacities;
step two: calculating the input-output stability attribute of each subsystem in the three-output power system;
step three: calculating the stability criterion of the interconnected system according to the input-output stability attribute of the subsystem;
step four: obtaining quantitative evaluation indexes reflecting the voltage stability of the interconnected system according to the stability criterion of the interconnected system, wherein the quantitative evaluation indexes reflecting the voltage stability of the interconnected system comprise stability quantitative evaluation indexes and safety quantitative evaluation indexes; evaluating the transient voltage stability of the power system according to the quantitative stability evaluation index, and judging whether the power system is stable; and evaluating the transient voltage safety of the power system according to the safety quantitative evaluation index, and judging whether the power system operates in a safety range.
Further, the process of establishing a three-output power system scene with different new energy permeabilities is as follows: and keeping the total power generation output of the three-output power system unchanged, and changing the power generation output of the new energy unit, so that the change of the new energy permeability is realized, and a three-output power system scene with different new energy permeabilities is obtained.
Further, the new energy permeability is calculated by the following formula:
Figure BDA0003467581400000021
further, a method for establishing a three-output power system scene with different direct current transmission capacities comprises the following steps: the third-sending power system comprises a first alternating current system, a second alternating current system and a third alternating current system, equivalent impedance of the first fixed electromotive force in series connection, equivalent impedance of the second fixed electromotive force in series connection, equivalent impedance of the third fixed electromotive force in series connection, equivalent impedance of the second alternating current system and the third alternating current system and equivalent impedance of the third alternating current system and the first alternating current system are kept unchanged, equivalent impedance of the first alternating current system and the second alternating current system is changed, and a third-sending power system scene with different direct current transmission capacities is obtained.
Further, in step two, the input-output stability attribute of each subsystem comprises a subsystem input-output gain γIOSAnd a quantity reflecting the input-output gain deviation
Figure BDA0003467581400000031
Further, the subsystem input-output gain γIOSCalculated by the following formula:
step 1, selecting a state variable x and an output y according to a mathematical model of a subsystem, selecting a per unit value of a terminal voltage as an output by a synchronous generator and a new energy unit, and selecting a per unit value of a terminal current as an output by a load;
step 2, giving safety and stability constraints of the subsystem;
step 3, determining the input signal u, the initial state x of the stationary subsystem0Obtaining output y by using a simulation method; given an input range of [0, a1]First input-output stability property γ1 IOSApproximated by the following equation:
Figure BDA0003467581400000032
step 4, by1,a2]Injecting the input signal according to the end point [ a ] of the first linear gain function1,b1]Second input-output stability property γ2 IOSEstimated as:
Figure BDA0003467581400000033
d2＝b1-a1l2
wherein, b1＝l1a1，b1Is the ordinate of the end point of the first progressive gain function, a1As the abscissa of the end point of the first progressive gain function, l1Is the slope of the 1 st progressive gain function;
step 5, byi-1,ai]Injecting the input signal according to the end of the last linear gain function [ a ]i-1,bi-1]To obtain all gamma at different inputsi IOSEstimated as:
Figure BDA0003467581400000034
di＝bi-1-ai-1li
wherein, bi-1＝li-1ai-1+di-1，bi-1Is the ordinate of the end point of the i-1 th progressive gain function, di-1Is the deviation value of the i-1 th progressive gain function, li-1Is the slope of the i-1 th progressive gain function, liIs the slope of the ith progressive gain function;
step 6, obtaining maximum gamma in step 5i IOSStabilization property gamma for subsystem input-outputIOS。
Further, the interconnection system stability criteria include the following:
ρ(GIOS)<1
Z(Id-GIOS)-1(α0 IOS|x0|+ΓIOS·d)+d≤τ
in the formula, ρ (G)IOS) Representing a small gain matrix GIOSRadius of spectrum, GIOSRepresenting a small gain matrix;
z is the input-output connection matrix between the subsystems, IdIs a unit matrix, alpha0 IOSTo reflect the amount of input-output gain deviation,0is an initial state, gammaIOSIs the input/output gain matrix, d is the progressive gain deviation, and τ is the local input range of the system.
Further, the stability quantitative evaluation index λ is calculated by the following formula:
λ＝1-ρ(GIOS)
in the formula, ρ (G)IOS) Representing a small gain matrix GIOSRadius of spectrum, GIOSA small gain matrix is represented.
Further, the safety quantitative evaluation index μ is calculated by the following formula:
Figure BDA0003467581400000041
wherein h isiFor the ith local safety calculation, τiIs the ith local input range.
Compared with the prior art, the invention has the following beneficial effects:
according to the method, the system of different new energy permeability is constructed, and the stability of the system is quantized through the established indexes, so that the quantitative evaluation of the influence of the new energy permeability on the stability of the power grid can be realized. According to the invention, the transient voltage stability of the three-output system can be evaluated by constructing the three-output system with different direct current transmission capacities and quantifying the stability of the three-output system. And the safety and stability quantitative evaluation indexes are utilized, so that the safe and stable operation margin of the system can be reflected. The influence of the new energy permeability and the transmission capacity of the direct current system on the transient voltage stability of the power system is comprehensively considered.
Drawings
FIG. 1 is a schematic diagram of a single-output system with high-ratio new energy
FIG. 2 is a simplified schematic diagram of a single-feed system
FIG. 3 is a diagram of a three-outlet system model with a high percentage of new energy.
FIG. 4 is a simplified representation of a three-feed system model.
Fig. 5 is a process diagram of the bus voltage dynamic change of the direct current unipolar latching fault B1 under different new energy permeabilities.
Fig. 6 is a process diagram of bus voltage dynamic change of the direct current unipolar latching fault B1 under different direct current transmission capacities.
FIG. 7 is a flow chart of the present invention.
Detailed Description
The following embodiments of the present invention are provided, and it should be noted that the present invention is not limited to the following embodiments, and all equivalent changes based on the technical solutions of the present invention are within the protection scope of the present invention.
Referring to fig. 7, following the above technical solution, the present embodiment provides a method for evaluating transient voltage stability of a power system, which specifically includes the following steps:
the method comprises the following steps: and establishing three-output power system scenes with different new energy permeabilities and three-output power system scenes with different direct current transmission capacities.
The single-delivery system containing high-proportion new energy can be represented by figure 1, and the single-delivery system containing high-proportion new energy comprises a synchronous thermal power generator set, a fan, a photovoltaic new energy source set, a load and a direct current circuit. According to the Davining theorem, new energy source units such as synchronous generator sets, fans, photovoltaic generators and the like in the alternating current system and load equivalence are in the form of constant electromotive force series equivalent impedance, and then a simplified single-output system is obtained, as shown in figure 2.
Three single-output power systems are connected with a transmitting end converter station through a connection impedance Z12、Z23、Z31The three-output power system can be obtained by parallel connection, and the three-output power system model can be represented as a system model shown in fig. 3. Wherein Z is12Equivalent impedance, Z, for connecting a first AC system 1 to a second AC system 223Equivalent impedance, Z, for connecting the second AC system 2 to the third AC system 331To connect the third ac system 3 to the equivalent impedance of the first ac system 1. In the three-output power system model, the transmitting-end converter stations work in a rectification state, and an alternating current system can be simplified into a form of fixed electromotive force series impedance through the Davining theorem. Wherein the first communication system 1 can be simplified to be fixedConstant electromotive force series equivalent impedance Z1The second ac system 2 can be simplified to a constant emf series equivalent impedance Z2The third ac system 3 can be simplified to a constant emf series equivalent impedance Z3Further, a three-output power system in a simplified form can be obtained, as shown in fig. 4.
The output of the new energy generator set is changed on the basis of the third-sending-out power system, so that a third-sending-out system containing high-proportion new energy with different new energy permeability can be obtained; varying equivalent impedance Z12Three-outlet systems containing high-proportion new energy with different direct current conveying capacities can be obtained, wherein the new energy permeability is as follows:
Figure BDA0003467581400000061
the specific method for constructing the three-output power system scene with different new energy permeability comprises the following steps: on the basis of the three-output power system model, the total power generation output of the system is kept unchanged, and the power generation output of the new energy unit is changed, so that the change of the new energy permeability is realized, and the three-output power system scene with different new energy permeabilities can be obtained.
The specific method for constructing three-output power system scenes with different direct current transmission capacities comprises the following steps: the DC transmission capacity of the three-output system is determined by the equivalent impedance Z of the system1、Z2、Z3、Z12、Z23、Z31Determining, maintaining, the system equivalent impedance Z1、Z2、Z3、Z23、Z31Constant, varying system equivalent impedance Z12And further, a three-output power system scene with different direct current transmission capacities is obtained.
Step two: calculating the input-output stability property gamma of each subsystem such as synchronous generator set, new energy source set and load in three-output power systemIOSAnd
Figure BDA0003467581400000062
γIOSis the input-output gain of the subsystem,
Figure BDA0003467581400000063
in order to reflect the amount of the input-output gain deviation, the specific process is as follows:
without loss of generality, consider a nonlinear system with external inputs:
Figure BDA0003467581400000064
y＝h(x,u)
wherein the content of the first and second substances,
Figure BDA0003467581400000065
input device
Figure BDA0003467581400000066
Function f: D → Rn，g:D→Rn×m. f and g are continuous with respect to x and satisfy the local Liphoz condition. f (0,0) ═ 0, h (0,0) ═ 0, and D and U respectively represent the state variables and the local regions of the external inputs.
Considering a non-linear system with external input, for any initial state x0E.g., D, and the input U e.U, if the following inequality holds, the system is said to satisfy the local output integral-integral estimation. Wherein alpha isIOS,
Figure BDA0003467581400000071
γIOS∈K∞。αIOSIs a quantity related to the system state quantity.
Figure BDA0003467581400000072
Calculating the input-output stable attribute gamma of the subsystem by adopting a simulation methodIOSThe specific process is as follows: to reduce conservation, a piecewise linear form of K is selected∞Function fitting gammaIOS. The expression of the piecewise asymptotic gain function w is as follows
Figure BDA0003467581400000073
Wherein the input field is divided into n subsets, [ a ]i-1,ai]Representing a subset of the ith external input.
Figure BDA0003467581400000074
An argument representing the progressive gain function,
Figure BDA0003467581400000075
a dependent variable representing an asymptotic gain function; a is1Is the maximum value of the 1 st external input, a2Is the maximum value of the 2 nd external input, ai-1Is the maximum value of the i-1 st external input, aiIs the maximum value of the ith external input, an-1Is the maximum value of the n-1 th external input, anIs the maximum value of the nth external input; l1Is the slope of the first progressive gain function,/2Is the slope of the second progressive gain function,/nIs the slope of the nth progressive gain function; d2Is the deviation value of the 2 nd progressive gain function, dnA deviation value of the nth progressive gain function; t is the integration time, y(s) is the output variable, u(s) is the input variable. Gamma rayIOSThe specific calculation process is described below.
Step 1, selecting a state variable x and an output y according to a mathematical model of a subsystem. Selecting a per unit value of the generator terminal voltage as output and selecting a per unit value of the terminal current as output by the synchronous generator and the new energy source unit;
step 2, considering the national regulation standard of the safe and stable operation of the independent power system, and giving the safe and stable constraint of the subsystem;
step 3, determining the input signal u, the initial state x of the stationary subsystem0And obtaining output y by using a simulation method. Given an input range of [0, a1]First input-output stability property γ1 IOSApproximated by the following equation:
Figure BDA0003467581400000076
step 4, by1,a2]Injecting the input signal according to the end point [ a ] of the first linear gain function1,b1]Second input-output stability property γ2 IOSEstimated as:
Figure BDA0003467581400000081
d2＝b1-a1l2
wherein, b1＝l1a1。b1Is the ordinate of the end point of the first progressive gain function, a1As the abscissa of the end point of the first progressive gain function, l1Is the slope of the 1 st progressive gain function.
Step 5, similar to step 4, by applying a pressure gradient in [ a ]i-1,ai]Injecting the input signal according to the end of the last linear gain function [ a ]i-1,bi-1]Further obtain all gamma under different inputsi IOSEstimated as:
Figure BDA0003467581400000082
di＝bi-1-ai-1li
wherein, bi-1＝li-1ai-1+di-1。bi-1Is the ordinate of the i-1 th progressive gain function end point. di-1Is the deviation value of the i-1 th progressive gain function, li-1Is the slope of the i-1 th progressive gain function, liIs the slope of the ith progressive gain function.
Step 6, selecting the maximum gamma obtained in the step 5IOSI.e. the required subsystem input-output stability property gammaIOS。
Similarly, subsystem input-output stabilization is obtained according to the following methodProperties
Figure BDA0003467581400000083
To further estimate the local area of the external input and initial state, the operating limit of the system state and output are chosen to be x, respectivelylimAnd ylim. Due to the function
Figure BDA0003467581400000084
In relation to the initial state of the non-linear system, for estimation
Figure BDA0003467581400000085
| x should be considered0A change in | is made. Let m1＝|x0|，
Figure BDA0003467581400000086
Wherein m is1Is a state variable, m2For integration of the system input, m3Is the integration of the system output. By varying m1And m2A series of points (m) can be obtained1,m2,m3) The following optimization problem is solved to estimate
Figure BDA0003467581400000087
minz＝g(m1)+w(m2)-m3
Figure BDA0003467581400000091
Wherein g is a predetermined approximation function
Figure BDA0003467581400000092
Is the resulting asymptotic gain function, and C is the set of points (m) resulting from the simulation1,m2,m3). Set of points (m) from simulation1,m2,m3) From the simulation results of (1), select
Figure BDA0003467581400000093
And | x0The maximum value of | is a local region of the external input and initial state, so that the system state and output are respectively kept at the operation limit xlimAnd ylimWithin.
Step three: in calculating the input-output stability property gamma of the subsystemIOSAnd
Figure BDA0003467581400000094
on the basis, the stability criterion of the interconnected system is calculated, and the specific process is as follows:
considering an interconnected system consisting of n subsystems, the mathematical model expression of the ith subsystem is as follows:
Figure BDA0003467581400000095
yi＝hi(xi,ui,ωi)
wherein the content of the first and second substances,
Figure BDA0003467581400000096
is the state variable of the ith subsystem,
Figure BDA0003467581400000097
and
Figure BDA0003467581400000098
input and output of the ith subsystem, ω, respectivelyiIs the input of the external disturbance to the ith subsystem.
The interconnection system stability criterion is as follows: if the following two conditions are met, the interconnected system is stable in input-output, which indicates that the voltage stability of the interconnected system is good.
1. The small gain condition being satisfied, i.e.
ρ(GIOS)<1
Wherein G isIOS＝ΓIOSZ，ΓIOSIs shaped like a gammaIOS＝diag(γi IOS) An input/output gain matrix of (a); gamma rayi IOSThe input and output gains of the subsystem i are obtained; z is an input-output connection matrix among the subsystems; ρ (G)IOS) Representing a small gain matrix GIOSRadius of spectrum, GIOSA small gain matrix is represented.
2. The following conditions hold:
Figure BDA0003467581400000099
wherein, IdIs a unit array; τ ═ τ [ τ ]1…τn]TFor local input range of the system, τ1For the 1 st local input range, τnIs the nth local input range; d ═ d1…dn]TFor progressive gain deviation, d1Is the deviation value of the 1 st progressive gain function, dnIs the deviation value of the nth progressive gain function.
Step four: obtaining quantitative evaluation indexes reflecting the voltage stability of the interconnected system according to the stability criterion of the interconnected system, wherein the quantitative evaluation indexes reflecting the voltage stability of the interconnected system comprise stability quantitative evaluation indexes and safety quantitative evaluation indexes; evaluating the transient voltage stability of the power system according to a quantitative evaluation index reflecting the voltage stability of the interconnected system, wherein the evaluation result can judge whether the system is stable; and evaluating the transient voltage safety of the power system according to the quantitative evaluation index reflecting the voltage safety of the interconnected system, wherein the evaluation result can judge whether the system operates in a safety range.
1. Stability quantitative evaluation index:
λ＝1-ρ(GIOS)
2. safety quantitative evaluation index:
Figure BDA0003467581400000101
wherein the content of the first and second substances,
Figure BDA0003467581400000102
hifor the ith local safety calculation, τiIs the ith local input range.
When the quantitative stability evaluation index is not satisfied, namely lambda is less than or equal to 0, the system is unstable; when the stability quantitative evaluation index meets, the larger the stability quantitative evaluation index lambda is, the larger the stability margin of the system is, and the better the stability is. When the safety and stability constraint condition is not satisfied, namely mu is less than or equal to 0, the system operates in an unsafe state; when the safety and stability constraint condition is met, the larger the safety quantitative evaluation index mu is, the larger the safety operation margin of the system is, and the better the safety is.
The following further illustrates the embodiments of the present invention by way of an example, which is only an example of the embodiments of the present invention, and the embodiments of the present invention are not limited thereto.
The effectiveness of the method is verified in a three-output power system containing a high proportion of new energy, and the structure of the method is shown in figure 3.
By using the method, the structure of the system is kept unchanged, the new energy permeability is changed, and the relationship between the new energy permeability and the transient voltage stability of the system is analyzed. And analyzing the dynamic change process of the voltage when the direct-current single-pole locking fault occurs in the three-sending-out system containing the high-proportion new energy when the permeability of the new energy is respectively 25%, 40% and 55%. First, when the new energy permeability of the system is 25%, based on the above estimation method, the maximum input τ of the system is calculated as [0.354,0.354,0.0053,0.192 ═ 0.354,0.354,0.0053,0.192]. Then, the calculated rho is 0.565<1, the small gain condition is satisfied, the system can return to a stable state after being disturbed, and the quantitative evaluation index of the stability is 0.435. And finally, judging whether the system operates in a safety constraint range on the basis of meeting the small gain condition. After the fault is removed, the initial state of the subsystem is | x0|＝[0.976,0.980,0.978,0.981,0.979]. Through calculation, the safety quantitative evaluation index is 0.335, the safety and stability constraint condition is met, and the system operation is not out of limit. By modifying the permeability of the new energy with different settings of the output of the fan and the photovoltaic, the initial state of the subsystem and the topological structure of the interconnected system are changed, and the stability and safety under different permeabilities of the new energy are improvedThe chemical evaluation index needs to be recalculated according to the flow. When the new energy permeability is 40% and 55%, the system stability quantitative evaluation indexes are 0.417 and 0.389 respectively, and the calculation results of the safety quantitative evaluation indexes are 0.316 and 0.290 respectively.
The results show that: when the system has direct current single-pole blocking fault, as the permeability of new energy is increased from 25% to 55%, the small gain condition and the safe operation constraint condition are always met, but the system stability quantitative evaluation index and the safety quantitative evaluation index are gradually reduced, and the system stability margin and the safe operation margin are continuously reduced. Under the scenes of the permeability of 25%, 40% and 55% of new energy, the voltage of a three-output power system containing high-proportion new energy can finally return to a new stable state after a direct-current single-pole locking fault occurs, and the dynamic process of the voltage is in a safe operation range. However, the overvoltage level of the system after the three-output system has the direct-current single-pole blocking fault increases along with the increase of the permeability of new energy, and the safe and stable operation margin of the system is reduced. Time domain simulation verified the analysis results, and the bus voltage dynamic variation of B1 is shown in FIG. 5.
And (3) keeping the permeability of the new energy unchanged, changing the system structure, and analyzing the relation between the direct current transmission capacity and the transient voltage stability of the system. Setting the new energy permeability to be 25% unchanged, and setting the impedance Z between the first alternating current system 1 and the second alternating current system 212The dynamic change process of the voltage during the dc single-pole blocking fault occurs at 0.15, 0.3, and 0.45, respectively. Impedance Z between the first AC system 1 and the second AC system 212The transmission power limits of the dc system 1 are 1.9100, 1.8621, 1.8386 at 0.15, 0.3, 0.45, respectively. Further, the impedance Z between the first alternating current system 1 and the second alternating current system 2 can be obtained by a quantitative evaluation method of the voltage stability of the three-output power system containing high-proportion new energy12The quantitative evaluation indexes of the system stability are 0.435, 0.427 and 0.419 respectively when the quantitative evaluation indexes of the system stability are 0.15, 0.3 and 0.45 respectively, and the calculation results of the quantitative evaluation indexes of the safety are 0.335, 0.329 and 0.321 respectively. This indicates that the system is safe and stable. The direct-current single-pole blocking fault of the B1 node is set for the three-condition system, and the transient voltage curve of the B1 node is observed and shown in FIG. 6.
The results show that: when the system is in DC single-pole locking, the impedance Z between the first AC system 1 and the second AC system 212The transmission power limits of the dc system 1 are 1.9100, 1.8621, 1.8386 at 0.15, 0.3, 0.45, respectively. The small gain condition and the safe operation constraint condition are always met, but the system stability quantitative evaluation index and the safety quantitative evaluation index are gradually reduced, and the system stability margin and the safe operation margin are continuously reduced. And thirdly, after the direct-current single-pole locking fault occurs in the power system, the voltage can finally return to a new stable state, and the dynamic process of the voltage is in a safe operation range. However, the overvoltage level of the system after the three-output system has the direct current single-pole latching fault is increased along with the reduction of the direct current transmission capacity, and the safe and stable operation margin of the system is reduced. Time domain simulation verified the analysis results, and the bus voltage dynamic variation of B1 is shown in FIG. 6.

Claims (9)

1. A method for evaluating transient voltage stability of a power system is characterized by comprising the following steps:
the method comprises the following steps: establishing three-output power system scenes with different new energy permeabilities and three-output power system scenes with different direct current transmission capacities;
step two: calculating the input-output stability attribute of each subsystem in the three-output power system;
step three: calculating the stability criterion of the interconnected system according to the input-output stability attribute of the subsystem;
step four: obtaining quantitative evaluation indexes reflecting the voltage stability of the interconnected system according to the stability criterion of the interconnected system, wherein the quantitative evaluation indexes reflecting the voltage stability of the interconnected system comprise stability quantitative evaluation indexes and safety quantitative evaluation indexes; evaluating the transient voltage stability of the power system according to the quantitative stability evaluation index, and judging whether the power system is stable; and evaluating the transient voltage safety of the power system according to the safety quantitative evaluation index, and judging whether the power system operates in a safety range.
2. The method according to claim 1, wherein the process of establishing three-output power system scenarios with different new energy permeabilities comprises: and keeping the total power generation output of the three-output power system unchanged, and changing the power generation output of the new energy unit, so that the change of the new energy permeability is realized, and a three-output power system scene with different new energy permeabilities is obtained.
3. The method of claim 2, wherein the new energy permeability is calculated by the following formula:
Figure FDA0003467581390000011
4. the method of claim 1, wherein the method of creating three-output power system scenarios with different dc transmission capabilities comprises: the third-sending power system comprises a first alternating current system, a second alternating current system and a third alternating current system, equivalent impedance of the first fixed electromotive force in series connection, equivalent impedance of the second fixed electromotive force in series connection, equivalent impedance of the third fixed electromotive force in series connection, equivalent impedance of the second alternating current system and the third alternating current system and equivalent impedance of the third alternating current system and the first alternating current system are kept unchanged, equivalent impedance of the first alternating current system and the second alternating current system is changed, and a third-sending power system scene with different direct current transmission capacities is obtained.
5. The method according to claim 1, wherein in step two, the input-output stability attribute of each subsystem comprises a subsystem input-output gain γIOSAnd a quantity reflecting the input-output gain deviation
Figure FDA0003467581390000021
6. The method of claim 5, wherein the subsystem input-output gain γ is a linear gainIOSCalculated by the following formula:
step 1, selecting a state variable x and an output y according to a mathematical model of a subsystem, selecting a per unit value of a terminal voltage as an output by a synchronous generator and a new energy unit, and selecting a per unit value of a terminal current as an output by a load;
step 2, giving safety and stability constraints of the subsystem;
step 3, determining the input signal u, the initial state x of the stationary subsystem0Obtaining output y by using a simulation method; given an input range of [0, a1]First input-output stability property γ1 IOSApproximated by the following equation:
Figure FDA0003467581390000022
step 4, by1,a2]Injecting the input signal according to the end point [ a ] of the first linear gain function1,b1]Second input-output stability property γ2 IOSEstimated as:
Figure FDA0003467581390000023
d2＝b1-a1l2
wherein, b1＝l1a1，b1Is the ordinate of the end point of the first progressive gain function, a1As the abscissa of the end point of the first progressive gain function, l1Is the slope of the 1 st progressive gain function;
step 5, byi-1,ai]Injecting the input signal according to the end of the last linear gain function [ a ]i-1,bi-1]Get different inputsAll of gammai IOSEstimated as:
Figure FDA0003467581390000031
di＝bi-1-ai-1li
wherein, bi-1＝li-1ai-1+di-1，bi-1Is the ordinate of the end point of the i-1 th progressive gain function, di-1Is the deviation value of the i-1 th progressive gain function, li-1Is the slope of the i-1 th progressive gain function, liIs the slope of the ith progressive gain function;
step 6, obtaining maximum gamma in step 5i IOSStabilization property gamma for subsystem input-outputIOS。
7. The method of claim 1, wherein the interconnection system stability criterion comprises the following formula:
ρ(GIOS)<1
Figure FDA0003467581390000032
in the formula, ρ (G)IOS) Representing a small gain matrix GIOSRadius of spectrum, GIOSRepresenting a small gain matrix;
z is the input-output connection matrix between the subsystems, IdIs a unit matrix which is formed by the following steps,
Figure FDA0003467581390000033
to reflect the amount of input-output gain deviation, x0Is an initial state, gammaIOSIs the input/output gain matrix, d is the progressive gain deviation, and τ is the local input range of the system.
8. The method according to claim 1, wherein the stability quantitative evaluation index λ is calculated by the following formula:
λ＝1-ρ(GIOS)
in the formula, ρ (G)IOS) Representing a small gain matrix GIOSRadius of spectrum, GIOSA small gain matrix is represented.
9. The method according to claim 1, wherein the safety quantitative evaluation indicator μ is calculated by the following formula:
Figure FDA0003467581390000034
wherein h isiFor the ith local safety calculation, τiIs the ith local input range.
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