CN111654029A - Bearing feed-in scale evaluation method for receiving-end power grid under extra-high voltage alternating current-direct current multi-feed-in - Google Patents

Bearing feed-in scale evaluation method for receiving-end power grid under extra-high voltage alternating current-direct current multi-feed-in Download PDF

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CN111654029A
CN111654029A CN202010570394.XA CN202010570394A CN111654029A CN 111654029 A CN111654029 A CN 111654029A CN 202010570394 A CN202010570394 A CN 202010570394A CN 111654029 A CN111654029 A CN 111654029A
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feed
receiving
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direct current
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郭建宇
黄泽华
耿翠英
王文豪
娄北
林烽
刘洋
张龙
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State Grid Corp of China SGCC
Economic and Technological Research Institute of State Grid Henan Electric Power Co Ltd
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Abstract

The invention discloses a bearing feed-in scale evaluation method for a receiving-end power grid under an extra-high voltage alternating current-direct current multi-feed-in, which belongs to the technical field of extra-high voltage power grid planning and operation and comprises the following steps: s1: constructing an evaluation index system of the load bearing alternating current and direct current feed-in scale of the receiving-end power grid, wherein the evaluation indexes comprise a receiving-end supporting capacity index, a static safety index and a transient safety index; s2: according to the evaluation index system in the S1, evaluating the load-bearing AC/DC feed-in scale of the receiving-end power grid; s3: according to the evaluation result of S2, the optimum plan is selected. According to the invention, an alternating current/direct current feed-in scale and proportion evaluation model for bearing of the receiving-end power grid based on a multi-index comprehensive evaluation method is established, and comprehensive and effective evaluation on the alternating current/direct current feed-in scale is realized.

Description

Bearing feed-in scale evaluation method for receiving-end power grid under extra-high voltage alternating current-direct current multi-feed-in
Technical Field
The invention relates to the technical field of planning and operation of an extra-high voltage power grid, in particular to a bearing feed-in scale evaluation method for a receiving-end power grid under extra-high voltage alternating current and direct current multi-feed-in.
Background
The reverse distribution characteristics of energy resources and load requirements in China are obvious. Coal resources mainly exist in north and west China, hydraulic resources mainly exist in south and west China, and oil and natural gas resources mainly exist in east, middle and west China and sea areas. The middle east region is the biggest load center in China. With the rapid development of national economy, the demand of power supply shows a rapid growth trend, and the contradiction of insufficient power supply in the developed area of the middle east economy is increasingly prominent. Meanwhile, along with the increasing attention of people to the environmental protection problems of energy conservation, emission reduction, haze treatment and the like, the power supply construction in the densely populated load center area is increasingly difficult. Therefore, the middle east power grid urgently needs to receive a large amount of external power through extra-high voltage alternating current and direct current engineering.
Due to the fact that the extra-high voltage alternating current and direct current drop point is high in power transmission power, the capacity of a single power transmission channel accounts for high proportion of load of a receiving-end power grid, an extra-high voltage direct current system needs the receiving-end alternating current power grid to provide reactive power support, and the like, and the characteristics of the power grid after the extra-high voltage alternating current and direct current drop point are more complex and variable. Therefore, the problem of coordination development of the extra-high voltage alternating current-direct current multi-feed back receiving-end power grid is urgently needed to be solved from the power grid planning level, systematic research is developed from the aspects of extra-high voltage alternating current-direct current multi-feed system characteristic analysis, receiving-end power grid carrying alternating current-direct current feed scale evaluation, receiving-end power grid optimization planning technology, power grid development economic and social effect evaluation and the like, a receiving-end power grid planning and evaluation key technology system suitable for extra-high voltage large-capacity alternating current-direct current multi-feed is constructed, and the safe, economic coordination and sustainable development of the receiving-end power grid. Therefore, the selection and evaluation of the bearing feed-in scale of the receiving-end power grid under the extra-high voltage alternating current and direct current multi-feed-in are crucial to power grid planning and operation.
The patent with the publication number of CN 109103916B discloses a method for evaluating the voltage supporting capability of a receiving end power grid of a multi-direct current feed-in system, and belongs to the technical field of power grid planning and operation of power systems. In order to solve the problem of accurate evaluation of the voltage supporting capability of the alternating-current power grid, firstly, measuring the alternating-current bus voltage fed in by each direct current of the power grid, the direct-current injection active power, the consumed reactive power and the bus voltage phase after the rated state and the current instruction change respectively; respectively obtaining a multi-feed-in equivalent effective short-circuit ratio and a multi-feed-in critical equivalent effective short-circuit ratio of each direct current according to the two measured values; and evaluating the voltage supporting capability of each direct current receiving end power grid by comparing the relative magnitude of the multi-feed-in equivalent effective short-circuit ratio and the multi-feed-in critical equivalent effective short-circuit ratio. The method can accurately evaluate the voltage supporting capability of the alternating current power grid under the conditions of synchronous change, asynchronous change and the like of each direct current in the multi-direct current feed-in system, and can provide a reference basis for the planning and construction of a large-scale alternating current and direct current hybrid system. However, the method only evaluates the supporting capacity of the receiving end of the power grid through the effective short-circuit ratio, has low evaluation dimension, and cannot comprehensively and accurately evaluate the load-bearing feed-in scale of the receiving end power grid.
The patent document with publication number CN 110070200A discloses a multi-index evaluation method and system for DC support strength of an AC power grid, which collects power flow and stability parameters of the power grid; calculating based on the collected power grid flow and stability parameters by combining preset evaluation indexes; evaluating the degree of the alternating current power grid to the direct current support based on the calculation result of the evaluation index, and taking a strengthening measure to the index of the weak degree of the direct current support; the preset evaluation index includes: a power transfer support strength index, a voltage support strength index, and a frequency support strength index. The direct current support strength degree multi-index evaluation method comprehensively considering the factors such as power transfer support strength, voltage support strength, frequency support strength and the like can provide comprehensive evaluation indexes for planning design and optimization of a multi-direct current feed-in power grid, and has the characteristics of simplicity, practicability and strong operability. However, the present invention still evaluates the degree of support strength and cannot solve the above technical problems.
Disclosure of Invention
In view of the above, the invention provides a method for evaluating the bearing feed-in scale of an extra-high voltage ac/dc multi-feed-in lower receiving-end power grid, aiming at the defects of the prior art.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the method for evaluating the bearing feed-in scale of the receiving-end power grid under the condition of extra-high voltage alternating current and direct current multi-feed-in comprises the following steps:
s1: constructing an evaluation index system of the receiving-end power grid bearing alternating current/direct current feed-in scale, wherein the evaluation index comprises a receiving-end supporting capacity index, a static safety index and a transient safety index;
s2: according to the evaluation index system in the S1, evaluating the AC/DC feed-in gauge borne by the receiving-end power grid;
s3: according to the evaluation result of S2, the optimum plan is selected.
Further, in S1, the receiving-end supporting capability index is a multi-feed short-circuit ratio, which is calculated by the following formula:
Figure BDA0002546103740000031
in the formula, i is a branch number; sacShort-circuit capacity, P, for DC-fed converter busdeqThe equivalent direct current power after the influence of other direct current loops is considered; zeqijFor an equivalent node impedance matrix Z looking into each DC conversion buseqThe ith row, the jth column element of,Pdiand PdjI, j return DC power.
Further, in S1, the static safety indicators include bus voltage out-of-limit, line and transformer overload, reactive support, peak shaving capability, and reserve capacity.
Further, the bus voltage out-of-limit is calculated by equations (2) to (4):
Figure BDA0002546103740000041
Figure BDA0002546103740000042
Figure BDA0002546103740000043
wherein, UiIs the voltage of the bus, n is the number of fault analyses,
Figure BDA0002546103740000044
the upper limit of the voltage is set as,
Figure BDA0002546103740000045
is the lower voltage limit;
line and transformer overload is calculated by formula (5):
Figure BDA0002546103740000046
wherein, l is the set of line and transformer, n is the failure frequency, SlIn order to overload the actual capacity of the component,
Figure BDA0002546103740000047
if the line power exceeds 80% of the rated power, the line is overloaded, and k is 0.8;
the reactive support is calculated by equation (6):
Figure BDA0002546103740000048
in the formula, theta is a reactive rotating standby generator set,
Figure BDA0002546103740000049
Qgmaximum reactive power and actual reactive power, Delta Q, of the generatorLThe maximum reactive variable quantity of the load. Wherein the content of the first and second substances,
Figure BDA00025461037400000410
and Δ QLAccording to empirical formula
Figure BDA00025461037400000411
And Δ QL＝0.8PL-QLPerforming an estimation of PgmaxAnd PLThe maximum active output and the active load of the generator are respectively;
the peak shaver capacity is calculated by equation (7):
Figure BDA00025461037400000412
wherein theta is a power grid peak shaving unit set,
Figure BDA00025461037400000413
for maximum output power of the generator, PgIs the actual power generation of the generator;
the spare capacity is calculated by equation (8):
Figure BDA0002546103740000051
wherein theta is a set of active rotating standby generators of the power grid,
Figure BDA0002546103740000052
for maximum power generation of the generator, PgActual active power output of the generator, PDmaxThe maximum active power shortage of the single-circuit direct-current line fault is obtained.
Further, in S1, the transient safety index includes a transient generator power angle difference and a transient voltage droop amplitude.
Further, the power angle difference of the generator is calculated by equation (9):
Figure BDA0002546103740000053
where θ is the set of faults, n is the number of fault settings, | θi-θjI represents the power angle difference of any two generators at a certain moment;
the transient voltage droop amplitude is calculated by equation (10):
Figure BDA0002546103740000054
wherein η is a bus set, m is the number of voltage drop buses, n is the number of fault settings,
Figure BDA0002546103740000055
is the per unit value of the lowest bus voltage in the fault.
Further, in S2, the method for evaluating the ac/dc feed-in load of the receiving-end power grid includes an entropy weight method and an improved analytic hierarchy process based on cluster analysis.
Further, the entropy weight calculation method comprises the following steps:
1) constructing an index matrix
Assuming that m feed-in scales are provided and the number of the evaluation indexes is n, calculating index values of all schemes under each index to obtain all index matrixes:
Figure BDA0002546103740000061
2) data normalization process
Because different indexes have different orders of magnitude and dimensions, the indexes are standardized firstly, the index values after the standardization are shown as the following formula, and the information content of the indexes after the standardization can be compared:
Figure BDA0002546103740000062
3) entropy of the calculation index
According to the definition of entropy in thermodynamics, the entropy of an index is as follows:
Figure BDA0002546103740000063
wherein:
Figure BDA0002546103740000064
4) computing entropy weights
The entropy weight of the index is the proportion of the entropy of the index in the sum of all the indexes, and thus the objective weight of the obtained index is as follows:
Figure BDA0002546103740000065
the improved analytic hierarchy process based on cluster analysis includes the following steps:
1) construction of an analytic hierarchy process structural model
Weighting the feed-in scale evaluation index into a target layer, a characteristic layer and an index layer, wherein the target layer is the subjective weight of the feed-in scale evaluation index, the characteristic layer refers to the accuracy, comprehensiveness, rapidity and practicability of the evaluation index, and the index layer is a specific quantitative index;
2) analytic hierarchy process calculation
Calculating the weight by an analytic hierarchy process, namely comparing the importance of the elements in the same layer to the elements in the upper layer, grading the relative importance by using quantified scales, calculating an importance sequence of the index according to the evaluation matrix, and further determining the subjective weight of the index;
the subjective weight of the index is calculated by an analytic hierarchy process and is as follows:
Figure BDA0002546103740000071
wherein, ω iskWeight, ω, of the k-th property of the property layer to the target layerkjThe weight of the kth characteristic for the jth index.
Further, in S3, the method for selecting the optimal solution includes the following steps:
1) establishing a comprehensive index matrix
The method is the same as the first step of calculating the objective weight of the index by using an entropy weight method, and an index comprehensive matrix is constructed by using all index values of all schemes;
2) data normalization process
And carrying out standardization processing on the index data to obtain an index normalization matrix as shown in the following formula:
Figure BDA0002546103740000072
3) determining an ideal scenario
And selecting indexes of the ideal scheme from the X matrix to construct an ideal optimal scheme X + and an ideal worst scheme X-. For the high-quality index, selecting the maximum value of the index; for low goodness indicators, the minimum value of the indicator is selected. The ideal optimal scheme consists of the indexes, and otherwise, the ideal optimal scheme is the index of the worst scheme.
4) Calculating the distance between the alternative and the ideal
Defining the distance between each alternative solution and the ideal optimal solution and the ideal worst solution respectively as
Figure BDA0002546103740000081
And
Figure BDA0002546103740000082
Figure BDA0002546103740000083
Figure BDA0002546103740000084
5) best plan determination
The proximity to the ideal is defined as:
Figure BDA0002546103740000085
Cithe smaller the alternative is, the closer the alternative is to the ideal optimal solution, and the solutions are ranked according to the proximity, so that the most appropriate feed size is selected.
At present, according to an alternating current and direct current feed-in mode and the strength of a grid structure, 4 typical alternating current and direct current multi-feed-in receiving-end power grids mainly exist in China, including a Jingjin Jilu power grid, an alternating current receiving and strong receiving-end power grid, a Huadong power grid, a direct current receiving and strong receiving-end power grid, a Shandong power grid, an alternating current and direct current mixed receiving and strong receiving-end power grid and a Hunan south Hunan power grid, wherein the power receiving proportion is about 32% in the large power receiving mode, the large-scale power receiving and transmitting capacity is mainly represented as channel self-restraint, and the problems of channel transient stability, dynamic stability and thermal stability coexist. When the direct current power transmission and reception proportion is smaller, the stability problem is not outstanding, and the voltage stability problem can be caused by the increase of the long-term power transmission and reception proportion; with the continuous increase of the direct current transmission capacity, a large number of conventional power grid units are replaced, the rotational inertia level of the east China power grid system is continuously reduced, the frequency regulation capacity is reduced, high-power impact caused by direct current locking is caused, and the frequency problem is particularly prominent.
In the face of such a situation, the industry personnel can easily think of evaluating the supporting capability of the receiving end of the power grid to ensure the normal operation of the extra-high voltage multi-feed receiving end power grid, for example, an evaluation method of the voltage supporting capability of the receiving end power grid of the multi-direct current feed-in system disclosed in the patent document with the publication number of CN 109103916B, and an evaluation method and a system of the degree of the direct current supporting strength and weakness of the alternating current power grid disclosed in the patent document with the publication number of CN 110070200 a, both of the two patent documents solve the selection problem of the load-bearing feed-in scale of the existing receiving end power grid by evaluating the degree of the supporting strength of the receiving end, and can meet the evaluation of the load-bearing capability of the receiving end power grid.
The accuracy of the evaluation of the load-bearing feed-in scale of the receiving-end power grid is influenced by various factors, including evaluation indexes of the feed-in scale and analysis and evaluation of the evaluation indexes, and various analysis and evaluation methods exist, and how to select the analysis and evaluation method to match with the evaluation indexes and how to perform data correction and processing on the evaluation indexes in a targeted manner to obtain a comprehensive and effective alternating current/direct current feed-in scale evaluation system is difficult to realize for technicians in the field.
Compared with the prior art, the invention has the following beneficial effects:
according to the method for evaluating the bearing and feeding scale of the receiving-end power grid under the extra-high voltage alternating current and direct current multi-feeding, an evaluation index system for the bearing and feeding scale of the receiving-end power grid is constructed by selecting evaluation indexes, the alternating current and direct current feeding scale is evaluated, and the most appropriate feeding scheme is determined.
In the evaluation index of the invention, the net rack supporting capacity is reflected by the relative size relationship between the short-circuit capacity of the alternating current system and the direct current transmission power. For a multi-feed-in direct current system, a multi-feed-in short circuit ratio index can measure the receiving capacity of a receiving-end power grid with multiple loops of direct current simultaneously accessed to each loop of direct current, and the larger the multi-feed-in short circuit ratio index is, the stronger the receiving capacity of the receiving-end power grid to direct current transmission is; the static safety analysis is used for detecting whether the system meets various constraint conditions when the system is transited from the steady state before the fault to the steady state after the fault, and measuring the steady-state operation conditions of the power grid after different faults. The static state safety can be analyzed through N-1 checking, and the system stability is judged according to whether the line, the transformer and the bus voltage are overloaded or not after the N-1 fault occurs or not. In addition, the peak regulation capacity, the reserve capacity, the reactive power supporting capacity and the like of the system under the normal operation condition are also standards for measuring the stability of the system; whether power angle instability and voltage instability occur in the state change process after the system has an accident is a problem concerned by transient safety analysis. The power angle stability can be measured by the maximum power angle difference of the generator in the fault process, and the voltage stability is mainly reflected by the fluctuation condition of the bus voltage in the transient process. The feed-in scale meeting the requirement of system stability can be used for measuring the distance from the system to the stability limit by using the power angle difference index of the transient generator and the transient voltage drop amplitude.
According to the method, an evaluation index system of the receiving-end power grid bearing AC/DC feed-in scale is constructed, an entropy weight method and an improved analytic hierarchy process based on cluster analysis are applied on the basis to carry out analysis and evaluation, the entropy weight method carries out weight distribution on indexes by calculating the variation degree of each index, and the method is high in objectivity and accuracy; the analytic hierarchy process decomposes the decision process, and compares every two of the same-layer elements with the importance of the previous layer. And finally, calculating the importance degree of the elements at the lowest layer to the elements at the uppermost layer by weighted average according to the relative importance relation of the elements at each layer. Qualitative evaluation and quantitative analysis are taken into consideration to the analytic hierarchy process, the opinion of expert can be fully respected, the method has the characteristic of strong subjectivity, the operation is simple, the flexibility is strong, two kinds of analysis and evaluation are combined with each other, the synergistic effect is realized, and the efficiency of selecting the best feed-in scheme is greatly improved.
Drawings
FIG. 1 is a schematic diagram of an evaluation index system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an AC/DC multi-infeed power grid model in an embodiment of the present invention;
FIG. 3 is a schematic diagram of a hierarchical analysis method structure model in an embodiment of the present invention.
Detailed Description
In order to better understand the present invention, the following examples are further provided to clearly illustrate the contents of the present invention, but the contents of the present invention are not limited to the following examples. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details.
Example one
As shown in fig. 1 to 3, the method for evaluating the bearing feed-in scale of the receiving-end power grid under the ultra-high voltage alternating current and direct current multi-feed-in condition comprises the following steps:
s1: constructing an evaluation index system of the receiving-end power grid bearing alternating current/direct current feed-in scale, wherein the evaluation index comprises a receiving-end supporting capacity index, a static safety index and a transient safety index;
s2: according to the evaluation index system in the S1, evaluating the AC/DC feed-in gauge borne by the receiving-end power grid;
s3: according to the evaluation result of S2, the optimum plan is selected.
In S1, the receiving-end supporting capability index is a multi-feed short-circuit ratio, which is calculated by the following formula:
Figure BDA0002546103740000121
in the formula, i is a branch number; sacShort-circuit capacity, P, for DC-fed converter busdeqThe equivalent direct current power after the influence of other direct current loops is considered; zeqijFor an equivalent node impedance matrix Z looking into each DC conversion buseqRow i, column j element of (1), PdiAnd PdjI, j return DC power.
Multiple feed-in short circuit ratio KMSCRWhen the ratio is less than 2, the system is an extremely weak system; when 2 is in<KMSCR<3, the system is weak; when K isMSCR>And 3, the system is strong.
In S1, the static safety indexes include out-of-limit bus voltage, overload of lines and transformers, reactive support, peak regulation capability and spare capacity.
The bus voltage out-of-limit is calculated by the formulas (2) to (4):
Figure BDA0002546103740000122
Figure BDA0002546103740000123
Figure BDA0002546103740000124
wherein, UiIs the voltage of the bus, n is the number of fault analyses,
Figure BDA0002546103740000125
the upper limit of the voltage is set as,
Figure BDA0002546103740000126
is the lower voltage limit;
line and transformer overload is calculated by formula (5):
Figure BDA0002546103740000127
wherein, l is the set of line and transformer, n is the failure frequency, SlIn order to overload the actual capacity of the component,
Figure BDA0002546103740000128
if the line power exceeds 80% of the rated power, the line is overloaded, and k is 0.8;
the reactive support is calculated by equation (6):
Figure BDA0002546103740000131
in the formula, theta is a reactive rotating standby generator set,
Figure BDA0002546103740000132
Qgmaximum reactive power and actual reactive power, Delta Q, of the generatorLThe maximum reactive variable quantity of the load. Wherein the content of the first and second substances,
Figure BDA0002546103740000133
and Δ QLAccording to empirical formula
Figure BDA0002546103740000134
And Δ QL＝0.8PL-QLPerforming an estimation of PgmaxAnd PLThe maximum active output and the active load of the generator are respectively;
the peak shaver capacity is calculated by equation (7):
Figure BDA0002546103740000135
wherein theta is a power grid peak shaving unit set,
Figure BDA0002546103740000136
for maximum output power of the generator, PgIs the actual power generation of the generator;
the spare capacity is calculated by equation (8):
Figure BDA0002546103740000137
wherein theta is a set of active rotating standby generators of the power grid,
Figure BDA0002546103740000138
for maximum power generation of the generator, PgActual active power output of the generator, PDmaxThe maximum active power shortage of the single-circuit direct-current line fault is obtained.
In S1, the transient safety indicator includes a transient generator power angle difference and a transient voltage sag amplitude.
The power angle difference of the generator is calculated by equation (9):
Figure BDA0002546103740000139
where θ is the set of faults, n is the number of fault settings, | θi-θjI represents the power angle difference of any two generators at a certain moment;
the transient voltage droop amplitude is calculated by equation (10):
Figure BDA0002546103740000141
wherein η is a bus set, m is the number of voltage drop buses, n is the number of fault settings,
Figure BDA0002546103740000142
is the per unit value of the lowest bus voltage in the fault.
In S2, the evaluation method of the load-bearing AC/DC feed-in scale of the receiving-end power grid comprises an entropy weight method and an improved analytic hierarchy process based on cluster analysis.
The entropy weight method calculation method comprises the following steps:
1) constructing an index matrix
Assuming that m feed-in scales are provided and the number of the evaluation indexes is n, calculating index values of all schemes under each index to obtain all index matrixes:
Figure BDA0002546103740000143
2) data normalization process
Because different indexes have different orders of magnitude and dimensions, the indexes are standardized firstly, the index values after the standardization are shown as the following formula, and the information content of the indexes after the standardization can be compared:
Figure BDA0002546103740000144
3) entropy of the calculation index
According to the definition of entropy in thermodynamics, the entropy of an index is as follows:
Figure BDA0002546103740000151
wherein:
Figure BDA0002546103740000152
4) computing entropy weights
The entropy weight of the index is the proportion of the entropy of the index in the sum of all the indexes, and thus the objective weight of the obtained index is as follows:
Figure BDA0002546103740000153
the improved analytic hierarchy process based on cluster analysis includes the following steps:
1) construction of an analytic hierarchy process structural model
Weighting the feed-in scale evaluation index into a target layer, a characteristic layer and an index layer, wherein the target layer is the subjective weight of the feed-in scale evaluation index, the characteristic layer refers to the accuracy, comprehensiveness, rapidity and practicability of the evaluation index, and the index layer is a specific quantitative index;
2) analytic hierarchy process calculation
Calculating the weight by an analytic hierarchy process, namely comparing the importance of the elements in the same layer to the elements in the upper layer, grading the relative importance by using quantified scales, calculating an importance sequence of the index according to the evaluation matrix, and further determining the subjective weight of the index;
the subjective weight of the index is calculated by an analytic hierarchy process and is as follows:
Figure BDA0002546103740000154
wherein, ω iskWeight, ω, of the k-th property of the property layer to the target layerkjThe weight of the kth characteristic for the jth index.
In S3, the method for selecting the optimal solution includes the steps of:
1) establishing a comprehensive index matrix
The method is the same as the first step of calculating the objective weight of the index by using an entropy weight method, and an index comprehensive matrix is constructed by using all index values of all schemes;
2) data normalization process
And carrying out standardization processing on the index data to obtain an index normalization matrix as shown in the following formula:
Figure BDA0002546103740000161
3) determining an ideal scenario
And selecting indexes of the ideal scheme from the X matrix to construct an ideal optimal scheme X + and an ideal worst scheme X-. For the high-quality index, selecting the maximum value of the index; for low goodness indicators, the minimum value of the indicator is selected. The ideal optimal scheme consists of the indexes, and otherwise, the ideal optimal scheme is the index of the worst scheme.
4) Calculating the distance between the alternative and the ideal
Defining the distance between each alternative solution and the ideal optimal solution and the ideal worst solution respectively as
Figure BDA0002546103740000162
And
Figure BDA0002546103740000163
Figure BDA0002546103740000164
Figure BDA0002546103740000165
5) best plan determination
The proximity to the ideal is defined as:
Figure BDA0002546103740000171
Cithe smaller the alternative is, the closer the alternative is to the ideal optimal solution, and the solutions are ranked according to the proximity, so that the most appropriate feed size is selected.
Example two
The method for evaluating the bearing feed-in scale of the receiving-end power grid under the extra-high voltage alternating current-direct current multi-feed-in of the embodiment of the invention is different from the first embodiment in that: in S2, since personal factors such as non-uniform expert scoring standards and inconsistent opinions may cause unreasonable subjective weights calculated by the analytic hierarchy process in the first embodiment, in order to eliminate the influence of the personal factors, the report uses a clustering analysis method to improve the conventional analytic hierarchy process.
The main idea of the improvement method is to determine the weight of expert scoring according to the consistency of the expert evaluation matrixes and the number of the same type of evaluation matrixes. The consistency degree of the judgment matrix is high, the judgment matrix belongs to experts of which most people belong to the same cluster, and the more reliable the judgment matrix is, the larger the expert weight is. The calculation steps are as follows:
(ii) importance sequence clustering
② calculating cluster analysis expert weight
Computing expert consistency weight
Fourthly, calculating the weight of the expert
Calculating new importance sequence
The influence of personal factors of experts on importance evaluation can be eliminated by adding a new importance sequence calculated by the expert weights, and the new subjective weights of the indexes are as follows:
Figure BDA0002546103740000181
EXAMPLE III
Taking a certain power grid in 2019 as an example, the evaluation system is used for evaluating a plurality of feeding schemes, and the optimal feeding scale under the load scale is explored.
In 2019, two +/-800 kilovolt high-voltage direct-current lines are used for transmitting power to Zhejiang, namely the Xiluou-Jinhua and Ningxia-Shaoxing extra high-voltage direct-current lines with the scale of 1600 ten thousand kilowatts. The load scale is 3635 ten thousand kilowatts, and the feeding proportion is 44% under the condition that the transmission power of the fed-in two-circuit direct current line reaches the maximum value. On the basis, the output of the sending end machine set and the direct current transmission power are reduced, the starting of the receiving end machine set is increased, the feed-in proportion can be reduced, and different feed-in schemes are obtained.
TABLE 1 Extra-high voltage DC feed-in scheme for certain power grid
Unit: thousands of kilowatts
Power receiving scheme Load scale Zhejiang power generation Bijin DC power Ningshao DC power Ratio of received power
1 3635 1147 800 800 44％
2 3635 1789 594 594 33％
3 3635 2417 400 400 22％
(1) Feed-in scheme stability check standard
For the operation of the power grid at a certain feed-in scale, the stability requirements of the power grid must first be met. The stability check criteria are as follows:
(ii) static Security
1) And (5) converging the load flow calculation. The output of the generator in the system does not exceed a limit value.
2) The important 500 kV line of the power grid, after the extra-high voltage direct current incoming line digestion channel line has N-1 fault, the important bus voltage of the receiving end power grid is not out of limit, and the important line and the transformer are not overloaded.
Security of transient state
1) The important 500 KV line of the power grid, after the three permanent magnet fault occurs in the extra-high voltage direct current external incoming line absorption channel line, the system is not unstable.
2) After the extra-high voltage direct current bipolar locking fault is timely removed from the sending end generator, the system is not unstable.
(2) Feed-in scheme stability verification
According to the system stability check standard provided in the foregoing, important receiving-end lines are screened out according to a receiving-end power grid structure, a fault mode is determined, stability check is performed on three power receiving schemes, and the three schemes all meet the stability requirement. For space reasons, only scenario 2, i.e., a check result with a feed ratio of 33%, will be described below.
Static safety analysis of power grid
1) Tidal current analysis
The outlet current of the extra-high voltage direct current converter station is shown as the following table:
TABLE 2 DC convertor station outgoing lines and power flows
Unit: thousands of kilowatts
Extra-high voltage drop point Node 1 at the other side of the outgoing line Node 2 at the other side of the outgoing line Node 3 at the other side of the outgoing line
Jinhua tea Ningde brand medicine Hua skewer Yongkang medicine
Line active power 92×2 94×2 103×2
Shaoxing wine Lanting All north Tidal bore
Line active power 102×2 102×2 89×2
The receiving end critical section flow is shown in the following table:
TABLE 3 Critical section tidal current of receiving-end grid
Unit: thousands of kilowatts
Name of cross section Line Number of parallel loops Single loop line power
Cross section of Wanzhe River dribble-yang rich 2 51
Zhejiang Hu section Fenhu-Sanlin 2 18
Minzhe section Ningde-Jinhua 2 92
Thunberg Su section Wunan-bottle kiln 1 33
Under the normal operation mode, no overload phenomenon occurs on the line and the transformer with the voltage class of more than 500 kilovolts.
2) N-1 checking
In order to analyze the influence of the extra-high voltage alternating current and direct current access and the receiving end startup change on the static safety, N-1 check is carried out on an extra-high voltage power 500 kV absorption channel and an inter-provincial power transmission section, extra-high voltage input power flow transfer in an N-1 operation mode is analyzed, and the trend and the stability margin of the load change of the transfer channel are analyzed.
a. N-1 fault analysis of extra-high voltage direct current power absorption channel
In the outgoing line of the Xiluodi-Jinhua +/-800 kV DC line inversion station, the Jinhua-Yongkang single-line has the maximum power of 1033 kilowatts. And performing N-1 verification on the line, wherein the power flow transfer result is shown as a table.
TABLE 4 Jinhua-Yongkang 500 KV line N-1 tidal current transfer results
Unit: thousands of kilowatts
Figure BDA0002546103740000201
From the result of N-1, it can be seen that after the outlet N-1 of the extra-high voltage converter station fails, the tide is mainly transferred to the parallel branch circuits, because the grid structure is reasonably designed, the extra-high voltage falls into the power grid and then has more channels to be consumed, and all the circuits are in a light-load state in a normal operation mode, therefore, after one circuit is disconnected, even if most of the tide is transferred to the other circuit in parallel, the parallel circuit can not be overloaded. Similarly, the N-1 verification is carried out on other 500 kV lines of the Jinhua converter station and 500 kV lines of the Shaoxing converter station, and no overload condition occurs.
b. Receiving end key section N-1 four calibration
And N-1 verification is carried out on the listed key section lines, so that overload is not generated.
Electric network transient state safety analysis
The transient stability of the receiving-end power grid is mainly concerned about the mutual influence between the ultra-high voltage power transmission system and the receiving-end alternating current system, namely whether the blocking fault of the ultra-high voltage direct current system and the instability of the receiving-end alternating current system can be caused after the fault of the receiving-end alternating current system occurs, and whether the instability of the receiving-end alternating current system can be caused after the blocking fault of the ultra-high voltage direct current system or the fault of the ultra-high voltage alternating current power transmission system occurs. The transient stability of the alternative scheme is checked through a single fault of an alternating current-direct current system, a serious fault of a receiving end alternating current system and a bipolar locking fault of a direct current system.
1) Single fault of ac/dc system
The single fault of the alternating current system is divided into the following 2 types:
a. and (4) the important alternating current line three permanent magnet fault of the receiving end system.
b. And the outgoing line of the receiving end direct current inverter station has three permanent faults.
The single fault of the direct current system is as follows: and (4) locking the ultrahigh voltage direct current single pole.
The fault time sequence set by simulation is as follows: when the AC line fails for 0s, the three-phase switch at the front side of the failure is tripped for 0.1s, and the three-phase switch at the rear side of the failure is tripped for 0.12 s. Monopole blocking occurs on the direct current line 0s, and reactive compensation capacitors on two sides of the direct current line are cut off by 0.1 s.
Simulation results show that after the important AC line in Zhejiang province has three permanent faults, a receiving end system can be kept stable. After a single-pole locking fault occurs in the direct-current system, the system can be kept stable under the condition that a fault line and equipment are timely removed.
2) Serious fault of receiving end AC system
Serious faults of the receiving end alternating current system comprise:
a. and (4) a three-permanent-jump double-circuit fault of the important alternating current line at the receiving end.
b. And the outgoing line of the receiving end direct current converter station has a three-permanent-jump double-circuit fault of 500 kV line.
The fault sequence is as follows: 0s fault, 0.1s trip-out of the fault front side three-phase switch, 0.12s trip-out of the fault rear side three-phase switch and the other two-side three-phase switch of the circuit.
Simulation results show that after three-permanent-jump double-circuit faults occur in the receiving-end extra-high voltage alternating current line and the important 500 kV line, the power grid is kept stable.
3) Bipolar latch-up failure of DC system
Performing bipolar latching fault verification on the Taiyang mountain-Shaoxing and the xi Luo Du-Jinhua of the two extra-high voltage direct current transmission lines respectively, and setting a fault time sequence as follows:
0s is in fault, and 0.1s cuts off the reactive compensation capacitor at the transmitting end and the receiving end.
Simulation results show that after bipolar locking faults occur in the two systems, the receiving end reactive power compensation device is timely cut off, and the systems can be kept stable.
Evaluation of the feeding scheme:
(1) static safety index calculation
The static safety indexes comprise bus voltage out-of-limit indexes, line and transformer overload indexes, reactive support, peak regulation capacity and spare capacity.
(ii) failure set
The fault set of the bus voltage out-of-limit index and the line and transformer overload index calculation is as follows: for the N-2 fault of 500 kV lines of the Zhejiang important section and the direct-current power absorption channel.
Considering only the bus and the line above 220 kilovolt, the overload is considered when the load rate of the line exceeds 80%, and the overload is considered when the load of the transformer exceeds 85%.
② index calculation result
And performing N-2 checking on the ultrahigh voltage alternating current transmission line and the important 500 kV receiving end line. The calculation results of the bus voltage out-of-limit index and the line and transformer overload indexes are shown in the table.
TABLE 5 bus voltage out-of-limit and line and transformer overload index calculation results
Bus voltage out-of-limit Line transformer overload
Scheme 1 1802.1 8.3
Scheme 2 1504.7 4.9
Scheme 3 1344.5 9.2
From the results in the table, it can be seen that as the feeding scale increases and the output of the receiving-end generator set decreases, the out-of-limit level of the bus voltage of the power grid above 220 kv increases after the N-2 fault, and the increase of the extra-high voltage direct current scale adversely affects the voltage stability of the power grid. The overload level of the power grid line transformer is reduced firstly and then increased, when the scale of external direct current is large, the load rate of a line and a transformer near a direct current drop point is increased, the overload risk is large after a fault, and the load rate of a line near a power plant is increased due to the fact that the receiving end is started up to be increased when the external electric power is too small, and overload is easy to occur. The results of the peak shaving capacity and the spare capacity index of the power grid are shown in the table.
TABLE 6 Peak shaving Capacity and spare Capacity calculation results
Figure BDA0002546103740000231
Figure BDA0002546103740000241
With the increase of the feed-in scale, the output of the receiving-end generator set is reduced, the peak regulation capacity and the reserve capacity of the receiving-end system are obviously improved, and the change of the reactive compensation capacity is not obvious.
(2) Transient stability index calculation
The transient stability index comprises a transient generator power angle difference index and a transient voltage drop amplitude index.
Calculating conditions
The set of faults used to calculate the metrics includes the following faults:
1) three-phase short circuit of DC absorption AC channel
2) Three-phase short circuit of receiving-end important alternating current line
3) Extra-high voltage DC channel bipolar latch
The power generator power angle difference index value object comprises all the power generators of the receiving end system. The voltage drop amplitude index value object is the 10 buses with the lowest receiving end voltage, namely more than 220 kilovolts. The failure timing settings are the same as in section 3.3.2.
② index calculation result
The results of the calculation of the transient power angle difference index and the transient voltage sag amplitude index of the alternative scheme are shown in the table.
TABLE 7 transient power angle difference index and Voltage sag index calculation results
Figure BDA0002546103740000242
Figure BDA0002546103740000251
(3) Short circuit ratio index calculation
The calculation results of the multi-feed short-circuit ratio indexes of the two direct-current lines of Xiluoudu-Jinhua and Ningdong-Shaoxing under different schemes are shown in the table.
TABLE 8 alternate multiple feed-in short circuit ratio index calculation results
Ningdong-Shaoxing Xiluodi-Jinhua Multiple feed-in short circuit ratio indicator
Scheme 1 5.93 5.03 5.48
Scheme 2 7.91 6.71 7.31
Scheme 3 11.86 10.6 11.23
Under the same feed scale, the multi-feed short circuit ratio of the Nindong-Shaoxing direct current line is larger than that of the Xiluodi-Jinhua direct current line. The three-phase short-circuit capacity of the alternating-current bus of the Shaoxing converter station is larger, and the acceptance capacity of the alternating-current bus of the Shaoxing converter station on direct-current transmission is stronger. The power receiving scale is reduced, the multi-feed short circuit ratio of the two direct current lines is increased simultaneously, and when a direct current system breaks down, the receiving end alternating current system can keep stability better.
(4) Index weight
The results of calculating the weights of the indices are shown in the table. Since no expert investigation is performed, the present example only uses the index objective weight as the comprehensive weight.
TABLE 9 Objective weight calculation results for the indices
Voltage out-of-limit Overload (OVP) Reactive support Peak shaving ability
0.1140 0.1359 0.1084 0.1235
Power angle difference of generator Amplitude of voltage sag Short circuit ratio Spare capacity
0.1153 0.1332 0.1453 0.1244
(5) Scheme ordering and optimal scheme
The results of all alternative criteria values after normalization are shown in the table.
TABLE 10 alternative Total index normalization results
Voltage out-of-limit Overload (OVP) Reactive support Peak shaving ability
Scheme 1 0.4437 0.3878 0.3834 0.7638
Scheme 2 0.3093 0.1356 0.4111 0.2281
Scheme 3 0.2470 0.4766 0.2055 0.0081
Power angle difference of generator Amplitude of voltage sag Short circuit ratio Spare capacity
Scheme 1 0.4624 0.4403 0.1433 0.6059
Scheme 2 0.3421 0.3134 0.2550 0.2101
Scheme 3 0.1955 0.2463 0.6017 00405
The indexes of voltage out-of-limit, overload, power angle difference and transient voltage drop amplitude are low-priority indexes. The indexes of peak regulation capacity, spare capacity and short circuit ratio are high-quality indexes. According to the index calculation results of tables 3-10, the index values of the ideal optimal scheme and the ideal worst scheme are determined as shown in the tables.
TABLE 11 Ideal optimum, worst case scenario terms
Voltage out-of-limit Overload (OVP) Reactive support Peak shaving ability
Best mode 0.2470 0.1356 0.4111 0.7638
Worst scheme 0.4437 0.4766 0.2055 0.0081
Power angle difference of generator Amplitude of voltage sag Short circuit ratio Spare capacity
Best mode 0.2463 0.1955 0.0617 06059
Worst scheme 0.4403 0.4624 0.1433 0.0405
The distance of the alternative from the ideal is calculated and the results are shown in the table below.
TABLE 12 distance of alternative from ideal
Distance from optimal solution Distance from the worst case Proximity of ideal plan
Scheme 1 0.2739 0.2103 0.5658
Scheme 2 0.2062 0.2550 0.4471
Scheme 3 0.2818 0.2554 0.5246
The feed-in scale comprehensive ranking is shown in the table according to the calculation result of the closeness of each scheme to the ideal scheme.
Table 13 feed Scale protocol Integrated ordering
Proximity of ideal plan Feed scale Ratio of received power Sorting
Scheme 1 0.496 4000×4 44％ 3
Scheme 2 0.6392 2968×4 33％ 1
Scheme 3 0.5223 2000×4 22％ 2
Under the condition that the load scale of a power grid is 3635 ten thousand kilowatts, the output of a generator set at a transmitting end and a receiving end is adjusted to obtain different extra-high voltage direct current feed-in scale schemes. And on the basis that the scheme meets the system stability condition, evaluating the scheme by using a comprehensive evaluation system. According to the actual calculation numerical values of the indexes, the peak load regulation capacity and the reserve capacity level of the power grid can be obviously improved by improving the external power scale, but certain adverse effects can be brought to the stability of a receiving end system, the overload risk after the N-2 fault is aggravated, the stability of the system in the transient process is also poorer, and the risk of direct current locking is increased due to the fact that direct current commutation failure is caused by the alternating current fault of the receiving end. The feed-in scale is too low, the power grid is started up to be enlarged, and the peak regulation capability of a receiving-end system is poor under the condition that direct current does not participate in peak regulation.
The method comprises the steps of firstly selecting 8 indexes such as overload, transient voltage safety margin, multi-feed short circuit ratio and the like to establish an evaluation index system of alternating current/direct current feed scale and proportion; secondly, calculating index comprehensive weight by using an entropy weight method and an improved analytic hierarchy process; and finally, calculating the distance between each scheme and the ideal optimal scheme and the ideal worst scheme based on the Euler distance, and sequencing different feed scales and proportions to determine the optimal scheme.
Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims (9)

1. The method for evaluating the bearing feed-in scale of the receiving-end power grid under the condition of extra-high voltage alternating current and direct current multi-feed-in is characterized by comprising the following steps of:
s1: constructing an evaluation index system of the load bearing alternating current and direct current feed-in scale of the receiving-end power grid, wherein the evaluation indexes comprise a receiving-end supporting capacity index, a static safety index and a transient safety index;
s2: according to the evaluation index system in the S1, evaluating the load-bearing AC/DC feed-in scale of the receiving-end power grid;
s3: according to the evaluation result of S2, the optimum plan is selected.
2. The method for evaluating the bearing and feeding scale of the receiving-end power grid under the condition of extra-high voltage alternating current and direct current multi-feeding as claimed in claim 1, wherein in S1, the receiving-end supporting capacity index is a multi-feeding short circuit ratio, and the multi-feeding short circuit ratio is calculated by the following formula:
Figure FDA0002546103730000011
in the formula, i is a branch number; sacShort-circuit capacity, P, for DC-fed converter busdeqThe equivalent direct current power after the influence of other direct current loops is considered; zeqijFor looking from each DC current conversion busThe entered equivalent node impedance matrix ZeqRow i, column j element of (1), PdiAnd PdjI, j return DC power.
3. The method for evaluating the load-bearing feed-in scale of the extra-high voltage alternating current-direct current multi-feed-in lower receiving-end power grid according to claim 2, wherein in S1, the static safety indexes comprise out-of-limit bus voltage, overload of circuits and transformers, reactive power support, peak regulation capacity and spare capacity.
4. The method for evaluating the bearing feed-in scale of the receiving-end power grid under the condition of extra-high voltage alternating current-direct current multi-feed-in according to claim 3, wherein the bus voltage out-of-limit is calculated by the following formulas (2) to (4):
Figure FDA0002546103730000021
Figure FDA0002546103730000022
Figure FDA0002546103730000023
wherein, UiIs the voltage of the bus, n is the number of fault analyses,
Figure FDA0002546103730000024
the upper limit of the voltage is set as,
Figure FDA0002546103730000025
is the lower voltage limit;
line and transformer overload is calculated by formula (5):
Figure FDA0002546103730000026
wherein, l is the set of line and transformer, n is the failure frequency, SlIn order to overload the actual capacity of the component,
Figure FDA0002546103730000027
if the line power exceeds 80% of the rated power, the line is overloaded, and k is 0.8;
the reactive support is calculated by equation (6):
Figure FDA0002546103730000028
in the formula, theta is a reactive rotating standby generator set,
Figure FDA0002546103730000029
Qgmaximum reactive power and actual reactive power, Delta Q, of the generatorLThe maximum reactive variable quantity of the load. Wherein the content of the first and second substances,
Figure FDA00025461037300000210
and Δ QLAccording to empirical formula
Figure FDA00025461037300000211
And Δ QL＝0.8PL-QLPerforming an estimation of PgmaxAnd PLThe maximum active output and the active load of the generator are respectively;
the peak shaver capacity is calculated by equation (7):
Figure FDA00025461037300000212
wherein theta is a power grid peak shaving unit set,
Figure FDA00025461037300000213
for maximum output power of the generator, PgIs the actual power generation of the generator;
the spare capacity is calculated by equation (8):
Figure FDA0002546103730000031
wherein theta is a set of active rotating standby generators of the power grid,
Figure FDA0002546103730000032
for maximum power generation of the generator, PgActual active power output of the generator, PDmaxThe maximum active power shortage of the single-circuit direct-current line fault is obtained.
5. The method for evaluating the load-bearing feed-in scale of the extra-high voltage alternating current-direct current multi-feed-in lower receiving-end power grid according to claim 3, wherein in S1, the transient safety indexes comprise the power angle difference of a transient generator and the transient voltage sag amplitude.
6. The method for evaluating the bearing feed-in scale of the receiving-end power grid under the condition of extra-high voltage alternating current and direct current multi-feed-in according to claim 5, wherein the power angle difference of the generator is calculated by a formula (9):
Figure FDA0002546103730000033
where θ is the set of faults, n is the number of fault settings, | θi-θjI represents the power angle difference of any two generators at a certain moment;
the transient voltage droop amplitude is calculated by equation (10):
Figure FDA0002546103730000034
wherein η is the bus bar set, m is the number of voltage drop bus bars, n is the number of fault settings,
Figure FDA0002546103730000035
is the per unit value of the lowest bus voltage in the fault.
7. The method for evaluating the bearing and feeding scale of the receiving-end power grid under the extra-high voltage alternating current-direct current multi-feeding condition according to claim 6, wherein in S2, the method for evaluating the bearing and feeding scale of the receiving-end power grid comprises an entropy weight method and an improved analytic hierarchy process based on cluster analysis.
8. The method for evaluating the bearing feed-in scale of the receiving-end power grid under the condition of extra-high voltage alternating current and direct current multi-feed-in according to claim 7, wherein the entropy weight method calculation method comprises the following steps:
1) constructing an index matrix
Assuming that m feed-in scales are provided and the number of the evaluation indexes is n, calculating index values of all schemes under each index to obtain all index matrixes:
Figure FDA0002546103730000041
2) data normalization process
Because the indexes have different orders of magnitude and dimensions, the indexes are firstly normalized, the index values after the normalization processing are shown as the following formula, and the information content of the normalized indexes can be compared:
Figure FDA0002546103730000042
3) entropy of the calculation index
According to the definition of entropy in thermodynamics, the entropy of an index is as follows:
Figure FDA0002546103730000043
wherein:
Figure FDA0002546103730000044
4) computing entropy weights
The entropy weight of the index is the proportion of the entropy of the index in the sum of all the indexes, and thus the objective weight of the obtained index is as follows:
Figure FDA0002546103730000051
the improved analytic hierarchy process based on cluster analysis includes the following steps:
1) construction of an analytic hierarchy process structural model
Weighting the feed-in scale evaluation index into a target layer, a characteristic layer and an index layer, wherein the target layer is the subjective weight of the feed-in scale evaluation index, the characteristic layer refers to the accuracy, comprehensiveness, rapidity and practicability of the evaluation index, and the index layer is a specific quantitative index;
2) analytic hierarchy process calculation
Calculating the weight by an analytic hierarchy process, namely comparing the importance of the elements in the same layer to the elements in the upper layer, grading the relative importance by using quantified scales, calculating an importance sequence of the index according to the evaluation matrix, and further determining the subjective weight of the index;
the subjective weight of the index is calculated by an analytic hierarchy process and is as follows:
Figure FDA0002546103730000052
wherein, ω iskWeight, ω, of the k-th property of the property layer to the target layerkjThe weight of the jth index to the kth characteristic.
9. The method for evaluating the bearing feed-in scale of the receiving-end power grid under the condition of extra-high voltage alternating current and direct current multi-feed-in according to claim 8, is characterized in that: in S3, the method for selecting the optimal solution includes the steps of:
1) establishing a comprehensive index matrix
The method is the same as the first step of calculating the objective weight of the index by using an entropy weight method, and an index comprehensive matrix is constructed by using all index values of all schemes;
2) data normalization process
And carrying out standardization processing on the index data to obtain an index normalization matrix as shown in the following formula:
Figure FDA0002546103730000061
3) determining an ideal scenario
And selecting indexes of the ideal scheme from the X matrix to construct an ideal optimal scheme X + and an ideal worst scheme X-. For the high-quality index, selecting the maximum value of the index; for low goodness indicators, the minimum value of the indicator is selected. The ideal optimal scheme consists of the indexes, and otherwise, the ideal optimal scheme is the index of the worst scheme.
4) Calculating the distance between the alternative and the ideal
Defining the distance between each alternative solution and the ideal optimal solution and the ideal worst solution respectively as
Figure FDA0002546103730000062
And
Figure FDA0002546103730000063
Figure FDA0002546103730000064
Figure FDA0002546103730000065
5) best plan determination
The proximity to the ideal is defined as:
Figure FDA0002546103730000066
Cithe smaller the alternative is, the closer the alternative is to the ideal optimal solution, and the solutions are ranked according to the proximity, so that the most appropriate feed size is selected.
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