CN115313529A - Electric energy quality assessment method considering spatial characteristics and alternating current-direct current two-side coupling effect - Google Patents

Electric energy quality assessment method considering spatial characteristics and alternating current-direct current two-side coupling effect Download PDF

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CN115313529A
CN115313529A CN202210939262.9A CN202210939262A CN115313529A CN 115313529 A CN115313529 A CN 115313529A CN 202210939262 A CN202210939262 A CN 202210939262A CN 115313529 A CN115313529 A CN 115313529A
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power quality
power
weight
coefficient
distribution network
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CN115313529B (en
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李志伟
王绪利
杨欣
吴晓鸣
张辉
郭汶璋
王明
秦亮
李鸿鹏
葛成
王磊
崔宏
钱龙
向阳
熊煜
种亚林
周帆
刘钊汛
刘开培
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Economic and Technological Research Institute of State Grid Anhui Electric Power Co Ltd
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Wuhan University WHU
Economic and Technological Research Institute of State Grid Anhui Electric Power Co Ltd
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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
    • H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • 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

The invention relates to a power quality evaluation method considering spatial characteristics and coupling action on both sides of alternating current and direct current, and compared with the prior art, the method overcomes the defect that the influence of the spatial characteristics and the coupling action on both sides of alternating current and direct current is not fully considered. The invention comprises the following steps: constructing an electric energy quality evaluation index set of an AC/DC power distribution network; calculating the weight of the alternating current side and the weight of the direct current side; solving the power quality index combination weight coefficient; calculating the power quality coupling coefficients of two sides of the AC/DC power distribution network; and (4) evaluating the electric energy quality of the AC/DC distribution network. According to the method, first weights under different regional characteristics and second weights under measured data are combined, an optimal combination weight is obtained by adopting an equalization algorithm, and the power quality indexes at two sides under the interactive influence of the network structures of the networks at two sides, the control strategy of the converter and the topological mechanism of the converter are considered, so that the power quality evaluation of the AC/DC distribution network under different scenes and under the coupling action is realized.

Description

Electric energy quality assessment method considering spatial characteristics and alternating current-direct current two-side coupling effect
Technical Field
The invention relates to the technical field of power grids, in particular to a power quality evaluation method considering space characteristics and alternating current-direct current two-side coupling effect.
Background
The access of a large amount of distributed energy (DG) and flexible load makes single alternating current distribution network or single direct current distribution network difficult the solution of overall consideration to the new problem that appears of electric wire netting, and the alternating current-direct current distribution network fuses both advantages each other simultaneously, has stronger reliability and more superior economic nature, has nevertheless also led to the complexity and the variety of its structure simultaneously. The problem of power quality existing in the traditional power distribution network is more emphasized in the alternating current-direct current power distribution network, and how to establish a scientific and more complete power quality evaluation system provides effective technical support for construction, planning, control and protection of the alternating current-direct current power distribution network.
The comprehensive evaluation research on the electric energy quality of the AC/DC power distribution network is mainly characterized by how to influence the electric energy quality index on the other side and how to balance the influence degree in an electric energy quality evaluation system when the unqualified electric energy quality index exists on one side.
In the conventional power quality evaluation method commonly used at present, although a combination weight method exists for evaluating the power quality, the combination weight coefficients are usually weighted by adopting normalization coefficients, and certain scientific basis is lacked; and meanwhile, the power quality coupling effect of the alternating current and the direct current is not considered.
How to make the combination weight more reasonable and incorporate the coupling effect into the electric energy quality assessment method of the AC/DC distribution network is a technical problem to be further solved.
Disclosure of Invention
The invention aims to solve the defect that the influence of the space characteristic and the coupling action on the two sides of alternating current and direct current is not fully considered in the prior art, and provides an electric energy quality evaluation method considering the space characteristic and the coupling action on the two sides of alternating current and direct current to solve the problems.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a power quality assessment method considering space characteristics and alternating current-direct current two-side coupling effect comprises the following steps:
constructing an electric energy quality evaluation index set of an AC/DC power distribution network;
calculating the weight of the alternating current side and the weight of the direct current side: classifying the AC/DC power distribution network according to the region type, respectively assigning values to the AC side power quality index and the DC side power quality index by an expert system according to the region type, and respectively determining a first weight of the AC side and a first weight of the DC side according to the assignment; acquiring data of the power quality indexes of each area, and respectively determining a second weight of an alternating current side and a second weight of a direct current side according to the acquired data;
solving the power quality index combination weight coefficient: combining the first weight and the second weight on the alternating current side or the direct current side respectively by adopting an equalization algorithm to obtain combined weights, and solving a combined weight optimal solution for the combined weights, wherein the combined weight optimal solution is a power quality index combined weight coefficient;
calculating the power quality coupling coefficients of two sides of the AC/DC power distribution network;
evaluating the electric energy quality of the AC/DC distribution network: obtaining the electric energy quality coefficient Z of the AC/DC distribution network com And according to the power quality coefficient Z com And evaluating the power quality of the AC/DC distribution network.
In the step of constructing the power quality evaluation index set of the AC/DC power distribution network, the power quality evaluation index set consists of n power quality indexes including n power quality indexes of an AC side power quality index and a DC side power quality index 1 Individual AC side power quality index and n 2 The power quality index of each direct current side, wherein n 1 The AC power quality measurement indexes at least comprise: voltage sag and short interruption, three-phase imbalance, harmonics, voltage fluctuations and flicker, frequency deviation, voltage deviation, n 2 The electric energy quality indexes of the direct current side at least comprise: voltage sags and short interruptions, voltage fluctuations and voltage deviations; n, n 1 、n 2 Are all positive integers.
The calculation of the alternating current side weight and the direct current side weight comprises the following steps:
dividing the region types, assigning n power quality indexes by an expert system according to the region types, and sequencing the power quality indexes of the alternating current side and the direct current side from large to small according to the assignment to obtain the sequenced power quality indexes, wherein the expression is as follows:
{s 1 |s 2 |…|s i |…|s m-1 |s m }，
wherein s is i Represents the ith power quality index, m = n 1 Or n 2 ，
When m = n 1 The time is an alternating current side power quality index, and when m = n 2 The time is a direct current side power quality index;
comparing two adjacent power quality indexes to obtain a power quality index relative ratio { a } after assignment 1 |a 2 |...|a i |...|a m-2 |a m-1 }，
Wherein a is i Is the power quality index s i Assigned value pair s i+1 The assigned ratio is called relative importance ratio;
establishing a judgment matrix F according to the relative importance degree ratio of the power quality index, wherein the judgment matrix F is as follows:
Figure BDA0003784853480000031
determining a first weight according to the evaluation matrix, wherein the first weight determination expression is as follows:
Figure BDA0003784853480000032
wherein, a i Is the power quality index s i Relative to s i+1 Relative importance ratio of; f is according to a i Obtaining a judgment matrix of m × m; m is the number of electric energy quality indexes, m = n 1 Or n 2 ；r ji Is the element of the jth row and ith column in the evaluation matrix;
Figure BDA0003784853480000034
representing the multiplication of elements in each column of the evaluation matrix F; w is a 1 Is a first weight and is a row vector containing m elements, wherein the ith column element is the weight of the ith power quality index;
acquiring power quality index { s) through sampling 1 |s 2 |...|s i |...|s m-1 |s m Sample value of, m = n 1 Or n 2 And sampling for M times to form an M X M electric energy quality index sampling matrix X, wherein each row is an electric energy quality index value obtained after one-time sampling:
Figure BDA0003784853480000033
when m = n 1 Then, the electric energy quality index sampling matrix X is the alternating current side electric energy index sampling matrix X alter When m = n 2 The electric energy quality index sampling matrix X is a direct current side electric energy index sampling matrix X direct ；
Carrying out normalization processing on the power quality index sampling matrix X to obtain a normalization matrix; solving the coefficient of variation for the normalized matrix using the expression:
Figure BDA0003784853480000041
in the formula (I), the compound is shown in the specification,
Figure BDA0003784853480000042
the average value of the ith column in the normalized power quality index sampling matrix X'; s i The coefficient of variation degree of the ith power quality index;
and solving the collision coefficient and the information carrying quantity by using a representation expression for the normalized matrix:
Figure BDA0003784853480000043
in the formula, R i The conflict coefficient of the ith power quality index and other power indexes is obtained; h i The information carrying quantity of the ith power quality index;
the second weight is derived using the expression:
Figure BDA0003784853480000044
in the expression, w 2 The second weight is a row vector containing m elements, wherein the ith column element is the weight of the ith power quality indicator, i =1,2.
The method for solving the power quality index combination weight coefficient comprises the following steps:
the set combining weight is expressed by the expression:
W＝αw 1 +βw 2
in the expression, w 1 Is a first weight, w, on the AC or DC side 2 The second weight is measured by alternating current or on the direct current side, and alpha and beta are linear combination coefficients;
the combination weight W is obtained by alternating current measurement of a first weight and a second weight combination or direct current measurement of the first weight and the second weight combination;
solving the combinatorial weight optimal solution W, i.e. W satisfies the expression
min(||W-w 1 ||+||W-w 2 ||)
Substituting the combination weight by the expression into the formula:
min(||αw 1 +βw 2 -w 1 ||+||αw 1 +βw 2 -w 2 ||)
s.t.α+β＝1，α，β≥0
in the expression, i | · | | represents the normal form calculation, and s.t. is a limiting condition;
obtaining alpha and beta, substituting alpha and beta into the combination weight to obtain the combination weight by the expressionThe optimal solution W, W is the row vector Q of 1*m 1 ，Q 2 ，...，Q i ...，Q m In which Q i A combination weight of m = n representing the ith power quality index 1 Or n 2 When m = n 1 The time expression is the combined weight coefficient W of the power quality indexes at the AC side alter When m = n 2 The time expression is the DC side power quality index combination weight coefficient W direct 。
The calculation of the power quality coupling coefficients of the two sides of the alternating current-direct current power distribution network comprises the following steps:
the expression of the power quality coupling coefficient of the two sides of the AC/DC distribution network is set as follows:
C＝G B G K G T
in the expression, C is the power quality coupling coefficient of the AC/DC distribution network, G B As a factor influencing the structural strength of the network, G K For converter control strategy influencing factor, G T Influence factors of the converter topological structure;
calculating G B ，G K ，G T The method comprises the following steps:
acquiring a power grid network structure strength influence factor;
network structure strength influence factor G of power grid B The expression is as follows:
Figure BDA0003784853480000051
in the formula, the electrical medium numbers of N branches of the power grid are arranged from small to large and are marked as B 1 To B N ，B l The number of the I power grid branches is the electrical betweenness, and N is the number of the power grid branches;
the electrical index B l The expression is shown as the following formula:
Figure BDA0003784853480000052
wherein G, L and F respectively represent power supply node and negativeA set of load nodes and distributed power nodes; w is a u Representing a weight for the ith grid branch power node u; w is a v Representing the weight to the l-th grid branch load node v; w is a k Representing the weight of the distributed power node k of the ith power grid branch, wherein u, v and k are positive integers; I.C. A uvk (i) Represents the current magnitude generated on branch l after unit current element is injected into the power-load-distributed power node pair (u, v, k);
acquiring a converter control strategy influence factor;
converter control strategy impact factor G K The expression is shown as the following formula:
Figure BDA0003784853480000061
in the formula, G K ' the influence coefficients of different control strategies on the electric energy quality index under the condition of combined operation are shown, and the control strategies of the converter are divided into three categories, T 1 Denotes the coefficient of influence, T, under constant power control 2 Expressing the coefficient of influence, T, of constant voltage and constant frequency control 3 Representing the influence coefficient under droop control;
acquiring a topological structure influence factor of the converter;
converter topology structure influencing factor G T As follows:
Figure BDA0003784853480000062
in the formula, S is the switching state of each bridge arm of the converter topology; Σ is the summation sign, meaning that all elements in the resulting vector are summed.
The evaluation of the electric energy quality of the alternating current-direct current distribution network comprises the following steps:
setting electric energy quality coefficient Z of AC/DC distribution network com ，
Electric energy mass coefficient Z com As follows:
Figure BDA0003784853480000063
in the formula, R 1 Is the ratio of the electric medium number of the AC side to the electric medium number of the AC/DC distribution network, R 2 The ratio of the electric medium number of the direct current side to the electric medium number of the alternating current and direct current distribution network; z alter Is the AC side power quality index coefficient, Z direct A direct current side power quality index coefficient; z k，cr The' is the electric energy quality index coefficient after the k-th obtained direct current side is transmitted to the alternating current side through the coupling effect, Z k，cr Transmitting the obtained AC side power quality index coefficient for the kth time to the power quality coefficient after the AC side power quality index coefficient is transmitted to the DC side through coupling action, wherein K is the set iterative computation time, and K =1,2. Σ denotes the sum of all the elements in the resulting vector,
Figure BDA0003784853480000064
calculating variable values in brackets from 1 to K for the value of K, and summing, wherein M is the sampling frequency of the power quality data;
electric energy quality coefficient Z of AC/DC distribution network com In the expression, the parameter acquisition method specifically adopts the following steps:
obtaining the ratio R of the electric permittivity of the AC side to the electric permittivity of the AC/DC distribution network 1 And the ratio R of the number of electrical terminals on the DC side to the number of electrical terminals on the AC/DC distribution network 2 The method comprises the following steps:
first, an electrical betweenness index B is used for each of an AC-side network and a DC-side network l Calculating the electrical permittivity of each branch and then summing to respectively obtain the electrical permittivity B of the AC side alter And the electric permittivity of the DC side B direct The electric dielectric coefficient B of the AC/DC distribution network is calculated by the following formula:
B＝B alter +B direct ，
ratio R of the number of electrical contacts on the AC side to the number of electrical contacts on the AC/DC distribution network 1 The following equation was used:
Figure BDA0003784853480000071
ratio R of the number of electrical gaps on the DC side to the number of electrical gaps on the AC/DC distribution network 2 The following equation is obtained:
Figure BDA0003784853480000072
obtaining AC side electric energy quality index coefficient Z alter And a DC side power quality index coefficient Z direct The method comprises the following steps:
AC side electric energy quality index coefficient Z alter Comprises the following steps:
Z alter ＝X alter W alter T
in the above formula, W alter T Combining a weight coefficient transposition matrix for the alternating-current side electric energy quality index; x alter An actual power quality index data matrix of an alternating current side is obtained;
Z direct ＝X direct W direct T
in the above formula, W direct T Combining a weight coefficient transposition matrix for the alternating-current side electric energy quality index; x direct The method comprises the steps of obtaining a direct current side actual electric energy quality index data matrix;
obtaining the power quality index coefficient Z of the direct current side after the power quality index coefficient is transmitted to the alternating current side through the coupling effect k，cr ', and the power quality index coefficient Z after the power quality index coefficient of the AC side is transmitted to the DC side through the coupling action k，cr The method comprises the following steps:
Z 1，cr ＝CZ alter ；
Figure BDA0003784853480000073
Z k,cr ＝CZ k-1,cr ′ k＝2,3,…K；
Figure BDA0003784853480000081
in the formula, C is the power quality coupling coefficient of the AC/DC distribution network;
according to the electric energy quality coefficient z of the AC/DC distribution network com The quality of the electric energy of the AC/DC distribution network is evaluated,
the quality of the electric energy of the AC/DC distribution network is divided into 5 grades: high quality, good, general, qualified and unqualified; according to the electric energy quality coefficient z of the AC/DC distribution network com And obtaining the electric energy quality grade of the AC/DC distribution network.
Advantageous effects
Compared with the prior art, the electric energy quality evaluation method considering the space characteristics and the coupling effect of the two sides of the alternating current and direct current combines the first weight under different regional characteristics with the second weight under the actual measurement data, adopts the equalization algorithm to obtain the optimal combination weight, considers the coupling effect of the electric energy quality indexes of the two sides under the interaction influence of the network structures of the networks at the two sides, the control strategy of the converter and the topological mechanism of the converter, realizes the electric energy quality evaluation of the alternating current and direct current distribution network under different scenes and the coupling effect, and enables the whole evaluation system to have more objectivity, scientificity and perfectness.
The invention also has the following advantages and positive effects:
1. the method is different from single alternating current power distribution network power quality evaluation and single direct current power distribution network power quality evaluation, and provides the concepts of different degrees of power quality indexes and mutual coupling action of alternating current and direct current side power quality indexes in different areas from different application scenes and the coupling action of alternating current and direct current sides, so that a unified evaluation method and an evaluation system are formed.
2. The method not only adopts an expert system to carry out weighting according to regional characteristics, but also carries out weighting according to measured data, simultaneously considers two weights, and adopts a method of balancing weights to solve an optimal solution, so that the combined weight is more accurate and reasonable.
3. According to the concept of the coupling coefficient of the alternating current side and the direct current side, the mechanism of mutual influence of the alternating current side and the direct current side is added during power quality evaluation, so that the evaluation is more accurate.
4. The invention combines the space characteristics, different weights and the AC/DC coupling effect by a more reasonable and scientific method, establishes a perfect AC/DC distribution network power quality evaluation method, and has good applicability.
Drawings
FIG. 1 is an overall flow chart of the present invention;
FIG. 2 is a topological diagram of the mechanism of the AC/DC distribution network of the present invention;
fig. 3 is a diagram showing an evaluation index set of the power quality of the ac/dc distribution network according to the present invention.
Detailed Description
So that the manner in which the above recited features of the present invention can be understood and readily understood, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings, wherein:
as shown in fig. 1 and fig. 2, the method for evaluating the quality of electric energy considering the spatial characteristics and the coupling effect between the ac side and the dc side according to the present invention includes the following steps:
s1, constructing an electric energy quality evaluation index set of the AC/DC distribution network.
The alternating current-direct current power distribution network is divided into an alternating current side power grid and a direct current side power grid, namely an alternating current side and a direct current side. The power quality evaluation index set consists of n power quality indexes including n1 power quality indexes at the alternating current side and n2 power quality indexes at the direct current side.
Wherein, n1 exchanges and surveys electric energy quality index and include at least: voltage sags and short interruptions; three phases are unbalanced; harmonics; voltage fluctuations and flicker; frequency deviation; voltage deviation, n2 direct current side electric energy quality indexes include at least: voltage sags and short interruptions, voltage fluctuations and voltage deviations.
S2, according to different electric energy quality indexes focused by different area types, carrying out area division and classification from the space, respectively carrying out assignment on the electric energy quality indexes of the alternating current side and the electric energy quality indexes of the direct current side by an expert system according to the area types, and respectively determining a first weight of the alternating current side and a first weight of the direct current side according to the assignment; acquiring data of the power quality indexes of each area, and respectively determining a second weight of an alternating current side and a second weight of a direct current side according to the acquired data; the method specifically comprises the following steps:
s21, determining a first weight of an alternating current side and a first weight of a direct current side;
dividing the region types into at least: industrial, office, commercial, residential, and agricultural areas.
The expert system assigns importance degrees to the n power quality indexes according to the region types, and then sorts the power quality indexes of the alternating current side and the direct current side from large to small according to the importance degree values to obtain sorted power quality indexes which are expressed as { s 1 |s 2 |...|s i |...|s m-1 |s m }，s i Represents the ith power quality index, m = n 1 Or n 2 When m = n 1 The time is an AC side power quality index, and when m = n 2 The time expression is the direct current side power quality index, then two adjacent power quality indexes are compared and assigned, and the ratio of the relative importance degree of the assigned power quality indexes is obtained and is { a 1 |a 2 |...|a i |...|a m-2 |a m-1 In which a is i Is the power quality index s i Importance value pair s i+1 The ratio of the importance values is referred to as a relative importance ratio.
Establishing a judgment matrix F according to the relative importance degree ratio of the power quality index, wherein the judgment matrix F is as follows:
Figure BDA0003784853480000101
determining a first weight from equation (1) according to the evaluation matrix, the first weight determining expression being:
Figure BDA0003784853480000102
in the formula (1), a i Is the power quality index s i Relative s i+1 Relative importance ratio of; f is according to a i Obtaining a judgment matrix of m × m; m is the number of the electric energy quality indexes, and m = n 1 Or n 2 ；r ji Is the element of the jth row and ith column in the evaluation matrix;
Figure BDA0003784853480000103
representing the multiplication of elements in each column of the evaluation matrix F; w is a 1 The first weight is a row vector containing m elements, wherein the ith column element is the weight of the ith power quality indicator.
S22, determining a second weight of the alternating current side and a second weight of the direct current side;
obtaining power quality index { s) through sampling 1 |s 2 |...|s i |...|s m-1 |s m Sample value of, m = n 1 Or n 2 And sampling for M times to form an M X M electric energy quality index sampling matrix X, wherein each row is an electric energy quality index value obtained after one-time sampling:
Figure BDA0003784853480000111
wherein, the element in the power quality index sampling matrix X uses X ji And the ith power quality index value of the jth sampling is represented.
When m = n 1 The power quality index sampling matrix X is the AC side power index sampling matrix X alter When m = n 2 The electric energy quality index sampling matrix X is a direct current side electric energy index sampling matrix X direct 。
The power quality index sampling matrix X is subjected to normalization processing, and the normalization processing is shown as a formula (2):
Figure BDA0003784853480000112
in formula (2), x' ji The element of the jth row and ith column in the normalized power quality index sampling matrix X' belongs to a positive index when the ith power quality index is larger and better, and belongs to a negative index when the ith power quality index is smaller and better;
Figure BDA0003784853480000113
the minimum value of an element in the ith column of the power quality index sampling matrix X is the minimum value of the ith power quality index in M times of sampling;
Figure BDA0003784853480000114
the maximum value of the element in the ith column, namely the maximum value of the ith power quality index in the M times of sampling.
And solving the variation coefficient of the normalized matrix as an expression (3):
Figure BDA0003784853480000115
in the formula (3), the reaction mixture is,
Figure BDA0003784853480000116
the average value of the ith column in the normalized power quality index sampling matrix X'; s. the i The coefficient of variation degree of the ith power quality index;
solving the collision coefficient and the information carrying quantity of the normalized matrix, wherein the collision coefficient and the information carrying quantity are represented by an expression (4):
Figure BDA0003784853480000121
in the formula (4), R i The conflict coefficient of the ith power quality index and other power indexes is obtained; h i Carrying quantity of information of the ith power quality index;
the second weight is obtained using equation (5):
Figure BDA0003784853480000122
in the formula (5), w 2 The second weight is a row vector containing m elements, wherein the ith column element is the weight of the ith power quality indicator, i =1,2.
And S3, combining the first weight and the second weight by adopting an equalization algorithm to obtain a combined weight, and solving an optimal solution W of the combined weight for the combined weight to enable the first weight and the second weight to reach a balanced state, namely the combined weight and the deviation sum of the combined weight are minimum, wherein the optimal solution W of the combined weight is a combined weight coefficient of the power quality index.
The combining weight is expressed by equation (6):
W＝αw 1 +βw 2 (6)
in the formula (6), w 1 Is a first weight, w 2 As a second weight, α and β are linear combination coefficients;
solving the optimal solution W of the combination weight, namely W satisfies the formula (7);
min(||W-w 1 ||+||W-w 2 ||) (7)
the formula (6) is introduced into the formula (7) to obtain:
Figure BDA0003784853480000123
in the formula (8), i | · | | represents the normal form calculation, and s.t. is a limiting condition.
And (5) obtaining alpha and beta according to the formula (8), and substituting the alpha and beta into the formula (6) to obtain the optimal solution W of the combination weight. W is the row vector Q of 1*m 1 ，Q 2 ，...，Q i ...，Q m In which Q i A combination weight of m = n representing the ith power quality index 1 Or n 2 When m = n 1 The time expression is the combined weight coefficient W of the power quality indexes at the AC side alter When m = n 2 The time expression is the combined weight coefficient W of the DC side power quality index direct 。
And S4, acquiring power quality coupling coefficients of two sides of the AC/DC power distribution network.
From the mechanism analysis of the AC/DC distribution network, it can be known that the power quality coupling coefficient is the result of the comprehensive action of the network structure strength of the power grid, the control strategy of the converter and the topological structure of the converter, and the expression is shown as formula (9):
C＝G B G K G T (9)
in formula (9), C is the power quality coupling coefficient of the AC/DC distribution network, G B For the structural strength influencing factor, G, of the network K For converter control strategy influencing factor, G T And the influence factor of the topological structure of the converter.
Wherein G is B ，G K ，G T The acquisition steps are as follows:
and S41, acquiring the influence factor of the network structure strength of the power grid.
The power grid structural strength is measured by the power grid uniformity, the index reflecting the power grid uniformity is a power grid network structural strength influence factor, the larger the index is, the weaker the power grid is, the more easily the influence on the opposite side power quality is, and the expression is as shown in formula (10):
Figure BDA0003784853480000131
in the formula (10), the electrical medians of the N branches of the power grid are arranged from small to large and are marked as B 1 To B N ，B l The number of the I-th power grid branch is the electrical betweenness, and N is the number of the power grid branches.
Because a large number of distributed power supplies are connected into the AC/DC power distribution network, after the distributed power supplies are considered to be connected, the conventional electrical betweenness index is improved, and the expression of the improved distributed power supplies is shown as a formula (11):
Figure BDA0003784853480000132
in the formula (11), G, L, and F respectively represent a set of a power node, a load node, and a distributed power node; w u Representing a weight for the ith grid branch power node u; w is a v For the ith gridThe weight of the branch load node v; wk represents the weight of the distributed power node k of the ith power grid branch, and can be directly obtained according to network topology and network parameters, wherein u, v and k are positive integers; i is uvk (l) The current magnitude generated on the branch l after the unit current element is injected into the power-load-distributed power node pair (u, v, k) is shown, and a specific value can be obtained through measurement.
And S42, acquiring the influence factor of the converter control strategy.
The converter control strategy is divided into two categories, namely joint operation and independent operation, wherein the AC-DC side coupling effect is considered under the condition of only joint operation. When the AC/DC distribution network is in combined operation, the control strategy of the converter has different influence degrees on the electric energy quality index, and the control strategy of the converter influences factor G K The expression is shown in formula (12):
Figure BDA0003784853480000141
in formula (12), G K ' the influence coefficients of different control strategies on the electric energy quality index under the condition of combined operation are shown, and the control strategies of the converter are divided into three categories, T 1 Denotes the coefficient of influence, T, under constant power control 2 Expressing the coefficient of influence, T, of constant voltage and constant frequency control 3 The influence coefficient under the droop control is represented, and the calculation mode is as the formula (13):
Figure BDA0003784853480000142
in formula (13), P ref For a given output active power, P represents the actual output active power, Q ref Representing a given output reactive power, Q representing the actual output reactive power; l represents a filter inductance parameter, and Ts represents sampling time; k ip Representing the coefficients P, K of a current loop compensated PI regulator pwm Representing a fundamental wave pulse modulation proportion coefficient, wherein s is a complex parameter in the Laplace transform; c represents the filter capacitance parameter, K q Denotes the reactive sag factor, K up Representing the coefficients P, K of a voltage loop compensated PI regulator ui Representing coefficients I, K of a voltage loop compensated PI regulator pp Representing the coefficient P of the power loop compensation PI regulator.
Only three common converter control strategies are considered, and if the converter control strategies are other special converter control strategies, the converter control strategy influence factor G K Set to 1, i.e. the converter control strategy impact is 1.
S43, acquiring the influence factor of the converter topological structure.
The current commonly used converter topology is a two-level converter, a three-level converter and G T As shown in expression (14):
Figure BDA0003784853480000151
in the formula (14), S is a matrix with 3 rows and 1 columns of switching states of each bridge arm of the converter topology, and can be obtained by concrete topology and modulation signals; Σ is a summation sign, meaning that the elements in the resulting vector are all added.
S5, obtaining the electric energy quality coefficient Z of the AC/DC power distribution network com And according to the power quality coefficient Z com The method for evaluating the electric energy quality of the AC/DC distribution network comprises the following specific steps:
s51, determining the electric energy quality coefficient Z of the AC/DC distribution network com 。
Considering the interaction of the power quality problems between the AC and DC power distribution networks, the power quality coefficient transmitted from one side power grid to the other side power grid through the coupling effect is circularly calculated for many times, so that the power quality coefficient Z com As shown in expression (15):
Figure BDA0003784853480000152
in the formula (15), R 1 Is the ratio of the electric medium number of the AC side to the electric medium number of the AC/DC distribution network, R 2 For a direct current side electric mediumThe ratio of the number to the number of electrical connections in the AC/DC distribution network; z alter Is the AC side power quality index coefficient, Z direct A direct current side power quality index coefficient; z k，cr The' is the electric energy quality index coefficient after the k-th obtained direct current side is transmitted to the alternating current side through the coupling effect, Z k，cr Transmitting the obtained AC side power quality index coefficient for the kth time to the power quality coefficient after the DC side power quality index coefficient is transmitted to the DC side through a coupling effect, wherein K is the set iterative computation time, and K =1,2. Σ represents the sum of all the elements in the resulting vector,
Figure BDA0003784853480000153
and calculating the variable values in brackets from 1 to K for the values of K, and summing, wherein M is the sampling times of the power quality data.
S52, obtaining the ratio R of the electric permittivity of the AC side to the electric permittivity of the AC/DC distribution network 1 And the ratio R of the number of electrical terminals on the DC side to the number of electrical terminals on the AC/DC distribution network 2 The method comprises the following steps:
firstly, the AC side network and the DC side network are respectively calculated by using the formula (11) in the step 4, and then the electric numbers of each branch are summed to respectively obtain the electric number B of the AC side alter And the electric permittivity of the DC side B direct The electrical permittivity B of the AC/DC distribution network is obtained by equation (16):
B＝B alter +B direct (16)
ratio R of the number of electrical contacts on the AC side to the number of electrical contacts on the AC/DC distribution network 1 The following equation (17) is obtained:
Figure BDA0003784853480000161
ratio R of the number of electrical gaps on the DC side to the number of electrical gaps on the AC/DC distribution network 2 The following equation (18) is obtained:
Figure BDA0003784853480000162
s53, obtaining the AC side electric energy quality index coefficient Z alter And a DC side power quality index coefficient Z direct The method comprises the following steps:
AC side electric energy quality index coefficient Z alter Comprises the following steps:
Z alter ＝X alter W alter T (19)
in the formula (19), W alter T Combining a weight coefficient transposition matrix for the alternating-current side electric energy quality index; x alter And the data matrix is an actual power quality index data matrix of the alternating current side.
Z direct ＝X direct W direct T (20)
In the formula (20), W direct T Combining the power quality indexes of the alternating current side with a weight coefficient transpose matrix; x direct And the data matrix is the actual power quality index data matrix of the direct current side.
S54, obtaining the electric energy quality index coefficient Z of the direct current side after the electric energy quality index coefficient is transmitted to the alternating current side through the coupling effect k，cr ', and the power quality index coefficient Z after the power quality index coefficient of the AC side is transmitted to the DC side through the coupling action k，cr The method comprises the following steps:
Z 1，cr ＝CZ alter ； (21)
Figure BDA0003784853480000163
Z k，cr ＝CZ k-1，cr ′ k＝2，3，...K； (23)
Figure BDA0003784853480000164
in the formula, C is the power quality coupling coefficient of the AC/DC distribution network.
S55, according to the power quality coefficient Z of the AC/DC distribution network com And evaluating the power quality of the AC/DC distribution network.
Obtained according to steps S51-54Electric energy quality coefficient z of AC/DC distribution network com According to the electric energy quality coefficient z of the AC/DC distribution network com Evaluating the power quality of the AC/DC power distribution network, and obtaining the power quality coefficient z of the AC/DC power distribution network com The smaller the power quality of the AC/DC distribution network, the better.
Further, the electric energy quality coefficient of the AC/DC distribution network can be classified into 5 grades: high quality, good, general, qualified and unqualified, and respectively corresponding electric energy quality coefficients Z of the AC/DC distribution network com The ranges are, as shown in table 1:
meter 1 Power quality coefficient and Power quality grade relation
Figure BDA0003784853480000171
Through grading the electric energy quality coefficient of the AC/DC distribution network, the electric energy quality of the AC/DC distribution network can be more intuitively embodied.
The method comprises the following steps of evaluating the power quality of a certain power grid in actual production:
step 1, as shown in fig. 3, according to the influence of the electric energy quality of a novel alternating current/direct current power distribution network, 8 electric energy quality indexes are selected as evaluation objects, and an electric energy quality evaluation index set of the alternating current/direct current power distribution network is constructed, wherein 6 alternating current measurement electric energy quality indexes comprise: voltage sags and short interruptions; three phases are unbalanced; harmonics; voltage fluctuations and flicker; frequency deviation; the voltage deviation, 2 direct current side power quality indexes include: voltage sags and short interruptions, voltage fluctuations and voltage deviations.
Step 2, assigning values to each power quality index by an expert system according to the region types, and determining a first weight of each power quality index according to the assignment; acquiring data of the power quality index of each region, and determining a second weight according to the acquired data; the method specifically comprises the following steps:
and S21, determining the first weight.
Taking an industrial area as an example, an expert system assigns importance degrees to n electric energy quality indexes, and then sorts the electric energy quality indexes of the alternating current side and the direct current side from large to small according to the importance degree values to obtain sorted electric energy quality indexes to form a judgment matrix F; the first weight is determined by equation (1) according to the evaluation matrix F, as shown in table 2.
And S22, determining a second weight.
Sampling values of the power quality indexes are obtained through sampling, 5 times of sampling are carried out totally, a power quality index sampling matrix X of 5*6 is formed, and each row is a power quality index value obtained after one-time sampling. The matrix X is sampled according to the power quality indicator, and a second weight is obtained by using equation (5), as shown in table 2.
TABLE 2 first and second weights of power quality index for industrial area
Figure BDA0003784853480000181
And 3, combining and solving the first weight and the second weight by adopting an equalization algorithm, and obtaining a combined weight optimal solution W of the first weight and the second weight in an equilibrium state by adopting an equation (6).
AC side electric energy quality index combination weight w alter ：
w alter ＝[0.384 0.137 0.118 0.116 0.118 0.126]
DC side power quality index combination weight W direct ：
w direct ＝[0.628 0.372]
In the formula, the power quality index combination weight w of the AC side alter From left to right are respectively voltage sag and short interruption, three-phase imbalance, harmonic waves, voltage fluctuation and flicker, frequency deviation and voltage deviation; DC side power quality index combination weight W direct From left to right are voltage sag and short break, voltage fluctuation and voltage deviation, respectively.
And 4, solving the power quality coupling coefficients on two sides of the AC/DC power distribution network by adopting an expression (9), wherein a converter control strategy adopts PQ control, and the converter is a three-level converter. The obtained C is:
Figure BDA0003784853480000191
step 5, establishing a whole AC/DC distribution network electric energy quality index evaluation system, carrying out comprehensive evaluation on the system, and obtaining an electric energy quality coefficient Z of the AC/DC distribution network according to a formula (15) com 。
Z com ＝2.036。
Further, in order to more intuitively reflect the power quality of the AC/DC power distribution network, the power quality grade of the AC/DC power distribution network is obtained according to the relation between the power quality coefficient and the power quality grade in the table 1.
In summary, the comprehensive assessment method for the electric energy quality of the alternating current and direct current power distribution network under the coupling action of the time-space characteristics and the two sides of the alternating current and direct current power distribution network is utilized to carry out scientific and reasonable comprehensive assessment on the electric energy quality of the alternating current and direct current power distribution network.
The foregoing shows and describes the general principles, principal features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (6)

1. A power quality assessment method considering space characteristics and alternating current-direct current two-side coupling effect is characterized by comprising the following steps:
11 Constructing an electric energy quality evaluation index set of the AC/DC distribution network;
12 Calculation of ac side weights and dc side weights: classifying the AC/DC power distribution network according to the region type, respectively assigning values to the AC side power quality index and the DC side power quality index by an expert system according to the region type, and respectively determining a first weight of the AC side and a first weight of the DC side according to the assignment; acquiring data of the power quality indexes of each area, and respectively determining a second weight of an alternating current side and a second weight of a direct current side according to the acquired data;
13 Solving the power quality index combination weight coefficient: combining the first weight and the second weight on the alternating current side or the direct current side respectively by adopting an equalization algorithm to obtain combined weights, and solving a combined weight optimal solution for the combined weights, wherein the combined weight optimal solution is a power quality index combined weight coefficient;
14 Calculating the power quality coupling coefficient of the two sides of the AC/DC distribution network;
15 Assessment of the power quality of the AC/DC distribution network: obtaining the electric energy quality coefficient Z of the AC/DC distribution network com And according to the power quality coefficient Z com And evaluating the power quality of the AC/DC distribution network.
2. The method for evaluating the quality of electric energy in consideration of the spatial characteristics and the coupling effect on the two sides of alternating current and direct current according to claim 1, wherein the method comprises the following steps: in the step of constructing the power quality evaluation index set of the AC/DC power distribution network, the power quality evaluation index set consists of n power quality indexes including n power quality indexes of an AC side power quality index and a DC side power quality index 1 Individual AC side power quality index and n 2 The power quality index of each direct current side is n 1 The AC power quality measurement indexes at least comprise: voltage sag and short interruption, three-phase imbalance, harmonics, voltage fluctuations and flicker, frequency deviation, voltage deviation, n 2 The direct current side power quality indexes at least comprise: voltage sags and short interruptions, voltage fluctuations and voltage deviations; n, n 1 、n 2 Are all positive integers.
3. The method for evaluating the quality of electric energy in consideration of the spatial characteristics and the coupling effect on the two sides of alternating current and direct current according to claim 1, wherein the method comprises the following steps: the calculation of the alternating current side weight and the direct current side weight comprises the following steps:
31 Dividing the region types, assigning n power quality indexes by an expert system according to the region types, and sequencing the power quality indexes of the alternating current side and the direct current side from large to small according to the assignment to obtain sequenced power quality indexes, wherein the sequence is represented as follows:
{s 1 |s 2 |...|s i |...|s m-1 |s m }，
wherein s is i Represents the ith power quality index, m = n 1 Or n 2 ，
When m = n 1 The time is an alternating current side power quality index, and when m = n 2 The time is a direct current side power quality index;
32 Two adjacent power quality indexes are compared to obtain the relative ratio of the power quality indexes after assignment as { a 1 |a 2 |...|a i |...|a m-2 |a m-1 }，
Wherein a is i Is the power quality index s i Assigned value pair s i+1 The assigned ratio is called relative importance ratio;
33 According to the relative importance ratio of the power quality index, establishing a judgment matrix F, wherein the judgment matrix F is as follows:
Figure FDA0003784853470000021
determining a first weight according to the evaluation matrix, wherein the first weight determination expression is as follows:
Figure FDA0003784853470000022
wherein, a i Is the power quality index s i Relative s i+1 Relative importance ratio of (a); f is according to a i Obtaining a judgment matrix of m × m; m is the number of the electric energy quality indexes, and m = n 1 Or n 2 ；r ji Is the element of the jth row and ith column in the evaluation matrix;
Figure FDA0003784853470000023
means for multiplying elements in each column of the evaluation matrix F; w is a 1 The first weight is a row vector containing m elements, wherein the ith column element is the weight of the ith power quality index;
34 Obtaining power quality indicator s by sampling 1 |s 2 |...|s i |...|s m-1 |s m Sample value of, m = n 1 Or n 2 And sampling for M times to form an M X M electric energy quality index sampling matrix X, wherein each row is an electric energy quality index value obtained after one-time sampling:
Figure FDA0003784853470000024
when m = n 1 The power quality index sampling matrix X is the AC side power index sampling matrix X alter When m = n 2 The electric energy quality index sampling matrix X is a direct current side electric energy index sampling matrix X direct ；
35 Normalizing the power quality index sampling matrix X to obtain a normalized matrix; solving the coefficient of variation for the normalized matrix using the expression:
Figure FDA0003784853470000031
in the formula (I), the compound is shown in the specification,
Figure FDA0003784853470000032
the average value of the ith column in the normalized power quality index sampling matrix X'; s i The coefficient of variation degree of the ith power quality index;
and solving the collision coefficient and the information carrying quantity by using a representation expression for the normalized matrix:
Figure FDA0003784853470000033
in the formula, R i The conflict coefficient of the ith power quality index and other power indexes is obtained; hi is the information carrying capacity of the ith power quality index;
the second weight is derived using the expression:
Figure FDA0003784853470000034
in the expression, w 2 The second weight is a row vector containing m elements, wherein the ith column element is the weight of the ith power quality indicator, i =1,2.
4. The method for evaluating the quality of electric energy considering the spatial characteristics and the ac-dc both-side coupling according to claim 1, wherein: the method for solving the power quality index combination weight coefficient comprises the following steps:
41 Set combining weights are expressed by the expression:
W＝αw 1 +βw 2
in the expression, w 1 Is a first weight, w, on the AC or DC side 2 The second weight is measured by alternating current or on the direct current side, and alpha and beta are linear combination coefficients;
the combination weight W is obtained by alternating current measurement of a first weight and a second weight combination or direct current measurement of the first weight and the second weight combination;
solving the combinatorial weight optimal solution W, i.e. W satisfies the expression
min(||W-w 1 ||+||W-w 2 ||)
Substituting the combination weight by the expression into the formula:
min(||αw 1 +βw 2 -w 1 ||+||αw 1 +βw 2 -w 2 ||)
s.t.α+β＝1，α，β≥0
in the expression, i | · | | represents the normal form calculation, and s.t. is a limiting condition;
to obtain alpha, beta, thenSubstituting alpha and beta into combination weight to obtain a row vector (Q) with W being 1*m and the optimal solution W of the combination weight from an expression 1 ，Q 2 ，...，Q i ...，Q m Denotes a combination weight of the ith power quality index, m = n 1 Or n 2 When m = n 1 The time expression is the combined weight coefficient W of the power quality indexes at the AC side alter When m = n 2 The time expression is the DC side power quality index combination weight coefficient W direct 。
5. The method for evaluating the quality of electric energy considering the spatial characteristics and the ac-dc both-side coupling according to claim 1, wherein: the calculation of the power quality coupling coefficients of the two sides of the alternating current-direct current power distribution network comprises the following steps:
51 Setting an expression of power quality coupling coefficients of two sides of an AC/DC distribution network as follows:
C＝G B G K G T
in the expression, C is the power quality coupling coefficient of the AC/DC distribution network, G B For the structural strength influencing factor, G, of the network K For converter control strategy influencing factor, G T Influence factors of the converter topological structure;
52 Calculate G) B ，G K ，G T The method comprises the following steps:
521 Obtaining a power grid network structure strength influence factor;
network structure strength influence factor G of power grid B The expression is as follows:
Figure FDA0003784853470000041
in the formula, the electrical medium numbers of N branches of the power grid are arranged from small to large and are marked as B 1 To B N ，B l The number of the I power grid branches is the electrical betweenness, and N is the number of the power grid branches;
the electrical index B l The expression is shown as the following formula:
Figure FDA0003784853470000051
in the formula, G, L and F respectively represent a set of a power supply node, a load node and a distributed power supply node; w is a u Representing a weight for the ith grid branch power node u; w is a v Representing the weight to the l-th grid branch load node v; wk represents the weight of the distributed power node k of the ith power grid branch, and u, v and k are positive integers; i is uvk (l) Represents the current magnitude generated on branch l after unit current element is injected into the power-load-distributed power node pair (u, v, k);
522 Obtaining a converter control strategy influence factor;
converter control strategy impact factor G K The expression is shown as the following formula:
Figure FDA0003784853470000052
in the formula, G K ' the influence coefficients of different control strategies on the electric energy quality index under the condition of combined operation are shown, and the control strategies of the converter are divided into three categories, T 1 Denotes the coefficient of influence, T, under constant power control 2 Expressing the coefficient of influence, T, of constant voltage and constant frequency control 3 Representing the influence coefficient under droop control;
523 Obtaining a converter topological structure influence factor;
converter topology structure influencing factor G T As follows:
Figure FDA0003784853470000053
in the formula, S is the switching state of each bridge arm of the converter topology; Σ is the summation sign, meaning that all elements in the resulting vector are summed.
6. The method for evaluating the quality of electric energy in consideration of the spatial characteristics and the coupling effect on the two sides of alternating current and direct current according to claim 1, wherein the method comprises the following steps: the evaluation of the electric energy quality of the alternating current-direct current distribution network comprises the following steps:
61 Setting the power quality factor Z of an AC/DC distribution network com ，
Electric energy mass coefficient Z com As follows:
Figure FDA0003784853470000054
in the expression, R 1 Is the ratio of the electric medium number of the AC side to the electric medium number of the AC/DC distribution network, R 2 The ratio of the electric medium number of the direct current side to the electric medium number of the alternating current and direct current distribution network; z alter Is the AC side power quality index coefficient, Z direct A direct current side power quality index coefficient; z k，cr The' is the electric energy quality index coefficient after the k-th obtained direct current side is transmitted to the alternating current side through the coupling effect, Z k，cr Transmitting the obtained AC side power quality index coefficient for the kth time to the power quality coefficient after the DC side power quality index coefficient is transmitted to the DC side through a coupling effect, wherein K is the set iterative computation time, and K =1,2. Σ denotes the sum of all the elements in the resulting vector,
Figure FDA0003784853470000061
calculating variable values in brackets from 1 to K for the value of K, and summing, wherein M is the sampling frequency of the power quality data;
62 Energy quality factor Z of AC/DC distribution network com In the expression, the parameter acquisition method specifically adopts the following steps:
621 Obtaining the ratio R of the electrical permittivity of the AC side to the electrical permittivity of the AC/DC distribution network 1 And the ratio R of the number of electrical terminals on the DC side to the number of electrical terminals on the AC/DC distribution network 2 The method comprises the following steps:
first, an electrical betweenness index B is used for each of an AC-side network and a DC-side network l To find out the branch powerAfter the number of the air channels is counted, summing is carried out to respectively obtain the number B of the electric channels on the alternating current side alter And the electric permittivity of the DC side B direct The electric dielectric coefficient B of the AC/DC distribution network is calculated by the following formula:
B＝B alter +B direct ，
ratio R of the number of electrical contacts on the AC side to the number of electrical contacts on the AC/DC distribution network 1 The following equation was used:
Figure FDA0003784853470000062
ratio R of the electric gap on the DC side to the electric gap on the AC/DC distribution network 2 The following equation is used:
Figure FDA0003784853470000063
63 Obtaining the AC side power quality index coefficient Z alter And DC side power quality index coefficient Z direct The method comprises the following steps:
AC side electric energy quality index coefficient Z alter Comprises the following steps:
Z alter ＝X alter W alter T
in the above formula, W alter T Combining a weight coefficient transposition matrix for the alternating-current side electric energy quality index; x alter An actual power quality index data matrix of an alternating current side is obtained;
Z direct ＝X direct W direct T
in the above formula, W direct T Combining a weight coefficient transposition matrix for the alternating-current side electric energy quality index; x direct The method comprises the steps of obtaining a direct current side actual electric energy quality index data matrix;
64 Obtaining the power quality index coefficient Z of the DC side after the power quality index coefficient is transmitted to the AC side through the coupling effect k，cr ', and the power quality index coefficient of the AC side is transmitted to the power quality system of the DC side through the coupling effectNumber Z k，cr The method comprises the following steps:
Z 1，cr ＝CZ alter ；
Figure FDA0003784853470000071
Z k，cr ＝CZ k-1，cr ′k＝2，3，...K；
Figure FDA0003784853470000072
in the formula, C is the power quality coupling coefficient of the AC/DC power distribution network;
65 According to the power quality coefficient Z of AC/DC distribution network com The quality of the electric energy of the AC/DC distribution network is evaluated,
the quality of the electric energy of the AC/DC distribution network is divided into 5 grades: high quality, good, general, qualified and unqualified; according to the electric energy quality coefficient Z of the AC-DC distribution network com And obtaining the electric energy quality grade of the AC/DC distribution network.
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