CN110556832B - Method and system for determining influence factors of cascading failure of alternating current and direct current power grid - Google Patents

Method and system for determining influence factors of cascading failure of alternating current and direct current power grid Download PDF

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CN110556832B
CN110556832B CN201910778968.XA CN201910778968A CN110556832B CN 110556832 B CN110556832 B CN 110556832B CN 201910778968 A CN201910778968 A CN 201910778968A CN 110556832 B CN110556832 B CN 110556832B
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entropy
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entropy value
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CN110556832A (en
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王震宇
焦瑞浩
王克非
丁剑
阴宏民
唐晓骏
侯凯元
张鑫
夏德明
宋云亭
尹路
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Northeast Branch Of State Grid Corp Of China
China Electric Power Research Institute Co Ltd CEPRI
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China Electric Power Research Institute Co Ltd CEPRI
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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
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Abstract

The invention discloses a method and a system for determining the influence factors of cascading failures of an alternating current and direct current power grid, wherein the method comprises the following steps: determining a typical fault subset corresponding to each line and enabling cascading faults to occur in the AC/DC power grid; and respectively calculating a power flow entropy value, a terminal frequency offset entropy value and a terminal voltage offset entropy value corresponding to each line when each typical fault in the corresponding typical fault subset occurs, and comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value with a preset critical entropy value vector to determine an influence factor of the alternating current and direct current power grid cascading faults when each line occurs to a certain typical fault. The method provides a technical means for quantitative analysis and evaluation of the influence factors of the cascading failure after the large-scale new energy grid connection, forms a judgment method capable of effectively reflecting the cause and the development process of the cascading failure of the power grid, can be applied to formulation of stability control measures for preventing the cascading failure, and has great significance for ensuring normal operation of the power grid after the intermittent new energy power supply is connected to the large scale.

Description

Method and system for determining influence factors of cascading failure of alternating current and direct current power grid
Technical Field
The invention relates to the technical field of safety and stability of an electric power system, in particular to a method and a system for determining influence factors of cascading failures of an alternating current-direct current power grid.
Background
In recent years, new energy power generation technology mainly based on wind power and photovoltaic in China is rapidly developed, with the increasing of installed capacity of new energy year by year and the increasing of direct current transmission projects in a power grid, a large number of electronic devices replace traditional power system electromagnetic conversion devices, so that energy structures and power systems in areas rich in clean energy are greatly changed, in a new power grid form, cascading failure modes and evolution processes of the system become more complex and changeable, and new challenges are brought to safe and stable operation of the power grid. At present, the interconnection of power grids of various large areas is realized through alternating current and direct current transmission lines, along with the gradual expansion of the networking range, the influence range of the power grids in cascading failure is further expanded, and the risk of large-area power failure caused by local failure is greatly increased. With the large-scale operation of extra-high voltage transmission projects and the continuous increase of clean energy installation, the frequency modulation and voltage regulation capability of the system is weaker due to the characteristic that the construction of a matched conventional power supply lags, the large-area disordered grid disconnection accident of the clean energy can be caused due to the insufficient frequency modulation and voltage regulation capability, and the cascading failure risk of the system is aggravated.
For different power systems, the form of the cascading failure is different due to different failure reasons and different operation conditions, so that the factors of the initial failure, the successive disconnection and the final cascading failure are different. If the power grid cascading failure cannot be controlled in time, the major power failure accident caused by the failure can greatly influence social economy, people's life and national stability. Therefore, the analysis and research on the cause and the influence factor of the cascading failure of the large-scale clean energy grid-connected power system are urgently needed to more clearly judge the cause and the development process of the cascading failure of the power grid, so that corresponding measures are made, and the risk of the cascading failure of the power grid is reduced.
Disclosure of Invention
The invention provides a method and a system for determining an influence factor of cascading failures of an alternating current and direct current power grid, and aims to solve the problem of how to determine the influence factor of the cascading failures of the alternating current and direct current power grid so as to reduce risks of the cascading failures of the power grid.
In order to solve the above problem, according to an aspect of the present invention, there is provided a method for determining an influence factor of a cascading failure of an ac/dc power grid, the method including:
according to a preset typical fault set, performing typical fault check on any line in the determined main line set of the alternating current and direct current power grid to determine a typical fault subset which corresponds to each line and enables the alternating current and direct current power grid to have cascading faults;
respectively calculating the power flow entropy value of the alternating current-direct current power grid when each line generates each typical fault in the corresponding typical fault subset;
respectively calculating a terminal frequency offset entropy value and a terminal voltage offset entropy value of a wind power base associated with each line when each typical fault in the corresponding typical fault subset occurs on each line and the line is cut off;
and comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value corresponding to each typical fault in the corresponding typical fault subset of each line with a preset critical entropy value vector to determine the influence factors of the alternating current and direct current power grid cascading faults when each line has a certain typical fault.
Preferably, wherein the preset set of typical faults comprises: the main protection fault comprises a single-phase permanent short-circuit fault, a three-phase permanent short-circuit fault, a double-circuit line different-name phase-to-phase short-circuit fault and a double-circuit line different-name phase-to-phase short-circuit fault.
Preferably, wherein calculating the power flow entropy value of the ac/dc power grid when any one of the corresponding typical fault subsets occurs for any one line comprises:
Figure BDA0002175963840000021
Figure BDA0002175963840000022
Figure BDA0002175963840000023
wherein, YPThe power flow entropy value of the alternating current and direct current power grid is obtained; zp(k) The load rate of the line is [ kb, (k +1) b]The line-rate sequence M [0, b,2 b. kb. mb]Mb is 1, and b is a preset constant; i is the total number of lines; alpha is alphaiThe load rate of the ith line; piActive power, P, carried for the ith lineN,iThe rated active power of the ith line.
Preferably, when any typical fault in the corresponding typical fault subset occurs on any line and the line is cut off, calculating a generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind turbine generator associated with the line by using the following modes:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
Figure BDA0002175963840000031
Figure BDA0002175963840000032
Figure BDA0002175963840000033
Figure BDA0002175963840000034
wherein, YfAnd YuA generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind power base respectively associated with the line; zfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguThe capacity of fan off-grid caused by the wind power base with the generator-end voltage deviation rate exceeding the preset voltage range; pgThe installed capacity of each wind power base; beta is aiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiThe terminal frequency of the ith wind power base is the terminal frequency of the ith wind power base; f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; u shapeiThe terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
Preferably, the following method is used for comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value corresponding to any one of the corresponding typical fault subsets of any line when any one of the line has any one of the corresponding typical fault subsets, with a preset critical entropy vector to determine the influencing factors of the line which cause the cascading faults of the alternating current and direct current power grid when the typical fault occurs, and the method includes:
constructing an entropy vector corresponding to any one of the typical faults in the corresponding typical fault subsets of any one line;
and comparing the entropy vector with corresponding entropy elements in a preset critical entropy vector one by one to determine a result vector, and determining the influence factors of the line which cause cascading failure of the alternating current and direct current power grid when the typical failure occurs according to the result vector.
Preferably, the comparing the entropy vector with corresponding elements in a preset critical entropy vector one by one to determine a result vector, and determining, according to the result vector, an influencing factor of the line which causes the cascading failure of the ac/dc power grid when the line has the typical failure includes:
Figure BDA0002175963840000041
Figure BDA0002175963840000042
wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure BDA0002175963840000043
is the result vector if Fp1, indicating that the influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
According to another aspect of the invention, there is provided a system for determining the impact factors of cascading failure of an ac/dc power grid, the system comprising:
the typical fault subset determining unit is used for performing typical fault check on any line in the determined main line set of the alternating current and direct current power grid according to a preset typical fault set so as to determine a typical fault subset which corresponds to each line and enables the alternating current and direct current power grid to have cascading faults;
the power flow entropy value determining unit is used for respectively calculating the power flow entropy value of the alternating current-direct current power grid when each line has each typical fault in the corresponding typical fault subset;
the frequency offset entropy and voltage offset entropy determining unit is used for respectively calculating a terminal frequency offset entropy value and a terminal voltage offset entropy value of the wind power base associated with each line when each typical fault in the corresponding typical fault subset occurs on each line and the line is cut off;
and the influence factor determining unit is used for respectively comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value corresponding to each typical fault in the typical fault subset corresponding to each line with a preset critical entropy value vector so as to determine the influence factor of the cascading faults of the alternating current and direct current power grid when a certain typical fault occurs in each line.
Preferably, wherein the preset set of typical faults comprises: the main protection fault comprises a single-phase permanent short-circuit fault, a three-phase permanent short-circuit fault, a double-circuit line different-name phase-to-phase short-circuit fault and a double-circuit line different-name phase-to-phase short-circuit fault.
Preferably, the power flow entropy determination unit calculates the power flow entropy of the ac/dc power grid when any one of the corresponding typical fault subsets occurs in any one line by using the following method, including:
Figure BDA0002175963840000051
Figure BDA0002175963840000052
Figure BDA0002175963840000053
wherein, YPThe power flow entropy value of the alternating current and direct current power grid is obtained; zp(k) The load rate of the line is [ kb, (k +1) b]The line-rate sequence M [0, b,2 b. kb. mb]Mb is 1, and b is a preset constant; i is the total number of lines; alpha is alphaiThe load rate of the ith line; piActive power, P, carried for the ith lineN,iThe rated active power of the ith line.
Preferably, the frequency offset entropy and voltage offset entropy determining unit calculates a generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind turbine generator associated with any line when any typical fault occurs in the corresponding typical fault subset and the line is cut off, by using the following method, including:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
Figure BDA0002175963840000054
Figure BDA0002175963840000055
Figure BDA0002175963840000061
Figure BDA0002175963840000062
wherein, YfAnd YuA generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind power base respectively associated with the line; zfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguThe capacity of fan off-grid caused by the wind power base with the generator-end voltage deviation rate exceeding the preset voltage range; pgThe installed capacity of each wind power base; beta is aiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiThe terminal frequency of the ith wind power base is the terminal frequency of the ith wind power base; f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; u shapeiThe terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
Preferably, the determining unit compares the power flow entropy, the frequency offset entropy and the voltage offset entropy corresponding to any one of the corresponding typical fault subsets of any one line when the fault occurs with a preset critical entropy vector to determine the influencing factor of the line causing the cascading fault of the ac/dc power grid when the fault occurs, including:
the entropy vector construction module is used for constructing an entropy vector corresponding to any one of the typical fault subsets corresponding to any one line when any one of the typical faults occurs;
and the influence factor determining module is used for comparing the entropy vectors with corresponding entropy elements in a preset critical entropy vector one by one to determine result vectors, and determining influence factors causing cascading failure of the alternating current and direct current power grid when the line has the typical failure according to the result vectors.
Preferably, the determining module of the influence factor compares the entropy vector with corresponding elements in a preset critical entropy vector one by one to determine a result vector, and determines the influence factor causing the cascading failure of the ac/dc power grid when the typical failure occurs in the line according to the result vector, including:
Figure BDA0002175963840000063
Figure BDA0002175963840000071
wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure BDA0002175963840000072
is the result vector if Fp1, indicating that the influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
The invention provides a method and a system for determining influence factors of cascading failures of an alternating current-direct current power grid, wherein the method comprises the following steps: determining a typical fault subset corresponding to each line and enabling cascading faults to occur in the AC/DC power grid; and respectively calculating a power flow entropy value, a terminal frequency offset entropy value and a terminal voltage offset entropy value corresponding to each line when each typical fault in the corresponding typical fault subset occurs, and comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value with a preset critical entropy value vector to determine an influence factor of the alternating current and direct current power grid cascading faults when each line occurs to a certain typical fault. On the basis of a traditional cascading failure tidal current entropy analysis method, the voltage entropy and the frequency entropy which can cause fan failure to be disconnected in successive disconnection are introduced, the comprehensive entropy vector for evaluating the influence factors of cascading failure is provided, the main influence factors causing the cascading failure of the system are determined through comparison with a safe and stable operation area, a technical means is provided for quantitative analysis and evaluation of the influence factors of the cascading failure after large-scale new energy grid connection, a judgment method capable of effectively reflecting the cause and the development process of the cascading failure of a power grid is formed, the method can be applied to formulation of a stability control measure for preventing the cascading failure, has great significance for guaranteeing normal operation of the power grid after intermittent new energy power supply is connected to the large scale, and is beneficial to the power grid to accept more new energy.
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A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
fig. 1 is a flowchart of a method 100 for determining an impact factor of a cascading failure of an ac/dc power grid according to an embodiment of the present invention; and
fig. 2 is a schematic structural diagram of a system 200 for determining an influence factor of a cascading failure of an ac/dc power grid according to an embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Fig. 1 is a flowchart of a method 100 for determining an influencing factor of a cascading failure of an ac/dc power grid according to an embodiment of the present invention. As shown in fig. 1, the method for determining the influence factors of the cascading failure of the ac/dc power grid according to the embodiment of the present invention introduces the voltage entropy and the frequency entropy that may cause the fan failure to be disconnected in successive switching on and off on the basis of the conventional cascading failure tidal current entropy analysis method, and provides the comprehensive entropy vector for evaluating the influence factors of the cascading failure, and determines the main influence factors causing the cascading failure of the system by comparing with the safe and stable operation region, so as to provide a technical means for quantitative analysis and evaluation of the influence factors of the cascading failure after the large-scale new energy grid connection, form a determination method capable of effectively reflecting the cause and the development process of the cascading failure of the power grid, be applied to the establishment of the stability control measures for preventing the cascading failure, and have great significance for ensuring the normal operation of the power grid after the intermittent new energy power supply is connected to the large scale, and the power grid is also facilitated to accept more new energy. The method 100 for determining the influence factors of the cascading failure of the alternating current and direct current power grid, which is provided by the embodiment of the invention, starts with a step 101, and performs typical failure check on any line in a determined main line set of the alternating current and direct current power grid according to a preset typical failure set in the step 101 so as to determine a typical failure subset corresponding to each line and enabling the alternating current and direct current power grid to have the cascading failure.
Preferably, wherein the preset set of typical faults comprises: the main protection fault comprises a single-phase permanent short-circuit fault, a three-phase permanent short-circuit fault, a double-circuit line different-name phase-to-phase short-circuit fault and a double-circuit line different-name phase-to-phase short-circuit fault.
In the embodiment of the invention, a main line in a power grid system and n lines in total near a new energy base are counted to form a line set L ═ { L ═ L1,l2,…,l nIn which lnRepresenting the nth line of the lines; then, each line in the line set L traverses single-phase permanent short-circuit fault, three-phase permanent short-circuit fault, double-circuit line different-name inter-phase short-circuit fault and double-circuit lineAnd determining typical faults such as main protection rejection and the like of the short-circuit fault between different phases of the line to determine a typical fault subset Sn corresponding to each line and enabling the alternating current-direct current power grid to have cascading faults, wherein n represents the nth line.
In step 102, a power flow entropy value of the ac/dc power grid is calculated for each line at the occurrence of each typical fault in the corresponding typical fault subset.
Preferably, wherein calculating the power flow entropy value of the ac/dc power grid when any one of the corresponding typical fault subsets occurs for any one line comprises:
Figure BDA0002175963840000091
Figure BDA0002175963840000092
Figure BDA0002175963840000093
wherein, YPThe power flow entropy value of the alternating current and direct current power grid is obtained; zp(k) The load rate of the line is [ kb, (k +1) b]The line-rate sequence M [0, b,2 b. kb. mb]Mb is 1, and b is a preset constant; i is the total number of lines; alpha is alphaiThe load rate of the ith line; piActive power, P, carried for the ith lineN,iThe rated active power of the ith line.
When a typical fault occurs in a certain line, the flow passing through the line is diverted, so that the power flow on other lines is changed, and when the power flow value reaches the action area of the installed protection equipment, the disconnection of other elements is caused, and the process is continuously carried out, so that cascading faults are caused. Therefore, whether the moisture distribution on the line of the power grid system is uniform is one of the key factors influencing the cascading failure of the system. Therefore, in the embodiment of the invention, the degree of uniformity of the power flow distribution on the system line is reflected by defining the power flow entropy.
In the embodiment of the present invention, the load factor α of the line is defined, and the calculation formula is as follows:
Figure BDA0002175963840000101
wherein, PiActive power, P, carried for the ith lineN,iAnd calculating the load rate of each line in the line set for the rated active power of the ith line through the public indication.
Then, a line load rate sequence M ═ 0, b,2b · · kb, · · mb is defined]Where mb is 1 and b is a constant. By LkIndicates that the load factor is in the load interval [ kb, (k +1) b]Number of upper lines, so that the load factor of the line is in the proportion Z of the intervalPComprises the following steps:
Figure BDA0002175963840000102
wherein Z isp(k) The load rate of the line is [ kb, (k +1) b]I is the total number of lines.
Finally, determining a power flow entropy function Y according to the definition of the entropy functionPComprises the following steps:
Figure BDA0002175963840000103
wherein, YPAnd the current entropy value is the current entropy value of the alternating current and direct current power grid. When the distribution of the power flow on the line is relatively uniform, namely the proportion of the load rate of the line in the power grid system in a certain interval is 1, namely Zp(k) When 1, Y is observedP0, minimum value; when the load rates of all lines are greatly different, the load flows of the lines are not uniformly distributed, Zp(k)<1, is known as YPWill be increased. Thus, in embodiments of the invention, a tide is usedAnd evaluating the risk of cascading failure caused by power flow transfer of the power grid by using the flow entropy value.
In step 103, the terminal frequency offset entropy and the terminal voltage offset entropy of the wind power base associated with each line when each typical fault in the corresponding typical fault subset occurs and the line is cut off are respectively calculated.
Preferably, when any typical fault in the corresponding typical fault subset occurs on any line and the line is cut off, calculating a generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind turbine generator associated with the line by using the following modes:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
Figure BDA0002175963840000111
Figure BDA0002175963840000112
Figure BDA0002175963840000113
Figure BDA0002175963840000114
wherein, YfAnd YuA generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind power base respectively associated with the line; zfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguFan caused by wind power base with machine end voltage deviation rate exceeding preset voltage rangeCapacity to be off-line; pgThe installed capacity of each wind power base; beta is aiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiThe terminal frequency of the ith wind power base is the terminal frequency of the ith wind power base; f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; ui is the generator terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
For one line, after a power grid with large-scale wind power access cuts off a certain fault element, for example, when a certain line has a three-permanent-N-1 fault, the terminal voltage of a wind power plant associated with the certain line is brought to 0, the fault ride-through capability of the certain line is exceeded, low-voltage grid disconnection of the wind power generation set is caused, the high-voltage grid disconnection of the wind power generation set is caused by the voltage rise at the moment of cutting off the fault line, power shortage is caused by continuous grid disconnection, and therefore the frequency problem of the system is caused, and grid disconnection of the wind power generation set is caused by frequency instability, so that a large power failure accident is caused; wherein the wind farm associated with the line is a wind farm in the vicinity of the line. Therefore, the frequency and voltage deviation affecting the wind turbine generator grid disconnection are also key factors affecting the cascading failure.
In the embodiment of the invention, for any typical fault corresponding to any line, a plurality of wind power bases G ═ G in the vicinity of the fault need to be determined1,g2,…gmAnd then determining the terminal frequency offset rate and the terminal voltage offset rate of each wind power base. For the ith wind power base, determining a generator end frequency offset rate and a generator end voltage offset rate by the following method:
Figure BDA0002175963840000121
Figure BDA0002175963840000122
wherein, betaiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiFor the ith wind power baseThe terminal frequency of (1); f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; u shapeiThe terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
Then, according to the preset allowable voltage deviation range [ beta ] of the fan under the condition of grid disconnectionmin,βmax]And the range of frequency deviation [ gamma ]min,γmax]Determining the wind power base beyond the non-grid-off range, and counting the capacity P of the fan off-grid caused by frequency deviationgfAnd capacity P of fan out of network due to voltage deviationguAnd determining the off-grid ratio of the fan caused by frequency offset and voltage offset by using the following formula:
Figure BDA0002175963840000123
Figure BDA0002175963840000124
wherein Z isfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguThe capacity of fan off-grid caused by the wind power base with the generator-end voltage deviation rate exceeding the preset voltage range; pgThe installed capacity of each wind power base; beta is aiAnd the terminal frequency deviation rate of the ith wind power base.
Finally, determining a generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind turbine generator set associated with the line by using a frequency offset entropy function and a voltage offset entropy function which are constructed according to the definition of the entropy function, wherein the method comprises the following steps:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
wherein, YfAnd YuAnd the terminal frequency offset entropy value and the terminal voltage offset entropy value of the wind power base respectively associated with the line.
When the fan is not off-line due to voltage and frequency offset, Z can be known from the above formulaf＝ZuWhen Y is equal to 0f＝Yu0, which is the minimum value, when the fan is off-line, ZfAnd ZuWill increase when Y isfAnd YuIt will also increase. Thus, in embodiments of the present invention, Y is utilizedfAnd YuThe value of (2) evaluates the fan off-grid condition, thereby evaluating the risk of cascading failure of the power grid due to frequency deviation and voltage deviation.
In step 104, comparing the power flow entropy, the terminal frequency offset entropy and the terminal voltage offset entropy corresponding to each typical fault in the corresponding typical fault subset occurring on each line with a preset critical entropy vector, so as to determine an influence factor of the cascading failure of the alternating current and direct current power grid when a certain typical fault occurs on each line.
Preferably, the following method is used for comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value corresponding to any one of the corresponding typical fault subsets of any line when any one of the line has any one of the corresponding typical fault subsets, with a preset critical entropy vector to determine the influencing factors of the line which cause the cascading faults of the alternating current and direct current power grid when the typical fault occurs, and the method includes:
constructing an entropy vector corresponding to any one of the typical faults in the corresponding typical fault subsets of any one line;
and comparing the entropy vector with corresponding entropy elements in a preset critical entropy vector one by one to determine a result vector, and determining the influence factors of the line which cause cascading failure of the alternating current and direct current power grid when the typical failure occurs according to the result vector.
Preferably, the comparing the entropy vector with corresponding elements in a preset critical entropy vector one by one to determine a result vector, and determining, according to the result vector, an influencing factor of the line which causes the cascading failure of the ac/dc power grid when the line has the typical failure includes:
Figure BDA0002175963840000131
Figure BDA0002175963840000132
wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure BDA0002175963840000133
is the result vector if Fp1, indicating that the influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
In the embodiment of the invention, the key factors of cascading failure mainly comprise three factors of moisture distribution and voltage offset and frequency offset of new energy power supply grid disconnection. In order to facilitate the analysis of the cause of the cascading failure of the system, the entropy vector is constructed by utilizing the entropy values obtained by calculation
Figure BDA0002175963840000141
Figure BDA0002175963840000142
Wherein, Yp、YfAnd YuThe power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value which correspond to the same line are respectively.
Then, the constructed entropy vector
Figure BDA0002175963840000143
And a predetermined vector of critical entropy values
Figure BDA0002175963840000144
The elements in the system are compared one by one to determine a result vector, and influence factors of cascading failures of the alternating current and direct current power grid when the typical failures occur to the line are determined according to the result vector. Wherein the predetermined critical entropy vector
Figure BDA0002175963840000145
Wherein Y ispsetThe threshold value is a tidal current entropy threshold value and represents a critical value of the next element disconnection or blackout accident caused by tidal current transfer at any moment; y isfsetThe threshold value is a frequency deviation entropy threshold value and represents a critical value of next fan offline caused by frequency deviation; y isusetThe threshold value of the voltage deviation entropy represents the critical value of next fan disconnection caused by the voltage deviation. And obtaining a region which is in a cuboid shape and is used for safely and stably operating the system by taking a preset critical value of the entropy vector as a boundary.
When making a comparison, if the entropy vector
Figure BDA0002175963840000146
If the system safety and stability area is not exceeded, the typical fault of the line at the moment can not cause the occurrence of the next-stage fault, namely, the cascading fault of the system can not be caused to cause the occurrence of the blackout accident.
If entropy vector
Figure BDA0002175963840000147
If the boundary of safe and stable operation of the system is exceeded, the fault at the moment can cause the next systemWhen the stage fault occurs, the risk of causing the cascading fault of the system to cause a blackout accident exists, and at the moment, the influence factor of causing the cascading fault of the system needs to be judged.
In the embodiment of the invention, in order to more intuitively judge the influence factors causing the cascading failure and the blackout accident, the piecewise function Fx and the vector are constructed
Figure BDA0002175963840000148
Figure BDA0002175963840000149
Figure BDA00021759638400001410
Wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure BDA0002175963840000151
is the result vector if Fp1, indicating that the influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
According to the vector
Figure BDA0002175963840000152
The influence factor discrimination table shown in the following table 1 can be obtained:
TABLE 1 determination of influencing factors
Vector F Determination of influence factor
(0,0,0) Is free of
(0,0,1) Offset of voltage
(0,1,0) Frequency offset
(1,0,1) Power flow transfer, voltage offset
(0,1,1) Voltage offset, frequency offset
(1,0,1) Power flow transfer, voltage offset
(1,1,0) Power flow transfer, frequency shift
(1,1,1) Power flow transfer, voltage offset, frequency offset
After determining the influence factors after the cascading failure is caused by a certain failure of a certain line, corresponding prevention and control measures can be made according to the influence factors to prevent the cascading failure of the system. The method comprises the following steps of (1) preventing cascading failures from occurring by improving the bearing capacity of a line under the condition that the cascading failures are caused by power flow transfer; for the condition that the voltage deviation and the frequency deviation cause the cascading failure of the system, the off-line of the new energy source unit is prevented by properly improving the fault ride-through capability of the new energy source unit, so that the cascading failure is reduced.
Fig. 2 is a schematic structural diagram of a system 200 for determining an influence factor of a cascading failure of an ac/dc power grid according to an embodiment of the present invention. As shown in fig. 2, a system 200 for determining an influence factor of a cascading failure of an ac/dc power grid according to an embodiment of the present invention includes: the fault diagnosis method comprises a typical fault subset determination unit 201, a power flow entropy value determination unit 202, a frequency offset entropy and voltage offset entropy determination unit 203 and an influence factor determination unit 204.
Preferably, the typical fault subset determining unit 201 is configured to perform typical fault check on any line in the determined main line set of the ac/dc power grid according to a preset typical fault set, so as to determine a typical fault subset corresponding to each line, where the ac/dc power grid is in cascading fault.
Preferably, wherein the preset set of typical faults comprises: the main protection fault comprises a single-phase permanent short-circuit fault, a three-phase permanent short-circuit fault, a double-circuit line different-name phase-to-phase short-circuit fault and a double-circuit line different-name phase-to-phase short-circuit fault.
Preferably, the power flow entropy determination unit 202 is configured to calculate a power flow entropy of the ac/dc power grid when each typical fault in the corresponding typical fault subset occurs in each line.
Preferably, the power flow entropy determination unit 202 calculates the power flow entropy of the ac/dc power grid when any one of the corresponding typical fault subsets occurs on any one line by using the following method, including:
Figure BDA0002175963840000161
Figure BDA0002175963840000162
Figure BDA0002175963840000163
wherein, YPThe power flow entropy value of the alternating current and direct current power grid is obtained; zp(k) The load rate of the line is [ kb, (k +1) b]The line-rate sequence M [0, b,2 b. kb. mb]Mb is 1, and b is a preset constant; i is the total number of lines; alpha is alphaiThe load rate of the ith line; piActive power, P, carried for the ith lineN,iThe rated active power of the ith line.
Preferably, the frequency offset entropy and voltage offset entropy determining unit 203 is configured to calculate a generator-side frequency offset entropy value and a generator-side voltage offset entropy value of the wind power base associated with each line when each typical fault in the corresponding typical fault subset occurs and the line is cut off.
Preferably, the frequency offset entropy and voltage offset entropy determining unit 203 calculates a generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind turbine generator associated with any line when any typical fault occurs in the corresponding typical fault subset and the line is cut off, by using the following method, including:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
Figure BDA0002175963840000171
Figure BDA0002175963840000172
Figure BDA0002175963840000173
Figure BDA0002175963840000174
wherein, YfAnd YuA generator end frequency offset entropy value and a generator end voltage offset entropy value of the wind power base respectively associated with the line; zfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguThe capacity of fan off-grid caused by the wind power base with the generator-end voltage deviation rate exceeding the preset voltage range; pgThe installed capacity of each wind power base; beta is aiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiThe terminal frequency of the ith wind power base is the terminal frequency of the ith wind power base; f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; u shapeiThe terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
Preferably, the influence factor determining unit 204 is configured to compare the power flow entropy, the terminal frequency offset entropy, and the terminal voltage offset entropy corresponding to each typical fault in the corresponding typical fault subset occurring in each line with a preset critical entropy vector, so as to determine an influence factor that the cascading faults occur in the ac/dc power grid when a certain typical fault occurs in each line.
Preferably, the determining unit 204 compares the power flow entropy, the frequency offset entropy and the voltage offset entropy corresponding to any one of the corresponding subset of typical faults occurring on any one line with a preset critical entropy vector to determine the influencing factor of the line causing the cascading fault of the ac/dc power grid when the typical fault occurs on the line, including:
the entropy vector construction module is used for constructing an entropy vector corresponding to any one of the typical fault subsets corresponding to any one line when any one of the typical faults occurs;
and the influence factor determining module is used for comparing the entropy vectors with corresponding entropy elements in a preset critical entropy vector one by one to determine result vectors, and determining influence factors causing cascading failure of the alternating current and direct current power grid when the line has the typical failure according to the result vectors.
Preferably, the determining module of the influence factor compares the entropy vector with corresponding elements in a preset critical entropy vector one by one to determine a result vector, and determines the influence factor causing the cascading failure of the ac/dc power grid when the typical failure occurs in the line according to the result vector, including:
Figure BDA0002175963840000181
Figure BDA0002175963840000182
wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure BDA0002175963840000183
is the result vector if FpIs 1, then representsThe influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
The system 200 for determining the influence factor of the cascading failure of the ac/dc power grid according to the embodiment of the present invention corresponds to the method 100 for determining the influence factor of the cascading failure of the ac/dc power grid according to another embodiment of the present invention, and details thereof are not repeated herein.
The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (12)

1. A method for determining influence factors of cascading failures of an AC/DC power grid is characterized by comprising the following steps:
according to a preset typical fault set, performing typical fault check on any line in the determined main line set of the alternating current and direct current power grid to determine a typical fault subset which corresponds to each line and enables the alternating current and direct current power grid to have cascading faults;
respectively calculating the power flow entropy value of the alternating current-direct current power grid when each line generates each typical fault in the corresponding typical fault subset;
respectively calculating a terminal frequency offset entropy value and a terminal voltage offset entropy value of a wind power base associated with each line when each typical fault in the corresponding typical fault subset occurs on each line and the line is cut off;
and comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value corresponding to each typical fault in the corresponding typical fault subset of each line with a preset critical entropy value vector to determine the influence factors of the alternating current and direct current power grid cascading faults when each line has a certain typical fault.
2. The method of claim 1, wherein the preset set of typical faults comprises: the main protection fault comprises a single-phase permanent short-circuit fault, a three-phase permanent short-circuit fault, a double-circuit line different-name phase-to-phase short-circuit fault and a double-circuit line different-name phase-to-phase short-circuit fault.
3. The method of claim 1, wherein calculating the entropy of the power flow of the ac/dc power grid for any one line in the event of any one of the corresponding subset of typical faults comprises:
Figure FDA0003408324030000011
Figure FDA0003408324030000012
Figure FDA0003408324030000013
wherein, YPThe power flow entropy value of the alternating current and direct current power grid is obtained; zp(k) The load rate of the line is [ kb, (k +1) b]The line ratio, load factor sequence M ═ 0, b,2b … kb, … mb]Mb is 1, and b is a preset constant; i is the total number of lines; alpha is alphaiThe load rate of the ith line; piActive power, P, carried for the ith lineN,iRated active power of the ith line; l iskIndicates that the load factor is in the load interval [ kb, (k +1) b]Number of upper lines.
4. The method of claim 1, wherein calculating a wind turbine end frequency offset entropy value and a wind turbine end voltage offset entropy value for any line associated with the line when any of the corresponding subset of typical faults occurs and the line is removed comprises:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
Figure FDA0003408324030000021
Figure FDA0003408324030000022
Figure FDA0003408324030000023
Figure FDA0003408324030000024
wherein, YfAnd YuGenerator-end frequency offsets of the wind power bases respectively associated with the lineShifting the entropy value and the terminal voltage offset entropy value; zfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguThe capacity of fan off-grid caused by the wind power base with the generator-end voltage deviation rate exceeding the preset voltage range; pgThe installed capacity of each wind power base; beta is aiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiThe terminal frequency of the ith wind power base is the terminal frequency of the ith wind power base; f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; u shapeiThe terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
5. The method according to claim 1, wherein comparing the power flow entropy, the terminal frequency offset entropy and the terminal voltage offset entropy corresponding to any typical fault in any typical fault subset corresponding to any line with a preset critical entropy vector to determine the influence factors of the line causing the cascading failure of the ac/dc power grid when the typical fault occurs includes:
constructing an entropy vector corresponding to any one of the typical faults in the corresponding typical fault subsets of any one line;
and comparing the entropy vector with corresponding entropy elements in a preset critical entropy vector one by one to determine a result vector, and determining the influence factors of the line which cause cascading failure of the alternating current and direct current power grid when the typical failure occurs according to the result vector.
6. The method according to claim 5, wherein the comparing the entropy vector with corresponding elements in a preset critical entropy vector one by one to determine a result vector, and determining, according to the result vector, an influencing factor of the line which causes cascading failure of the ac/dc power grid when the line has the typical failure includes:
Figure FDA0003408324030000031
Figure FDA0003408324030000032
wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure FDA0003408324030000033
is the result vector if Fp1, indicating that the influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
7. A system for determining the contributing factors of cascading failures in an ac/dc power grid, the system comprising:
the typical fault subset determining unit is used for performing typical fault check on any line in the determined main line set of the alternating current and direct current power grid according to a preset typical fault set so as to determine a typical fault subset which corresponds to each line and enables the alternating current and direct current power grid to have cascading faults;
the power flow entropy value determining unit is used for respectively calculating the power flow entropy value of the alternating current-direct current power grid when each line has each typical fault in the corresponding typical fault subset;
the frequency offset entropy and voltage offset entropy determining unit is used for respectively calculating a terminal frequency offset entropy value and a terminal voltage offset entropy value of the wind power base associated with each line when each typical fault in the corresponding typical fault subset occurs on each line and the line is cut off;
and the influence factor determining unit is used for respectively comparing the power flow entropy value, the terminal frequency offset entropy value and the terminal voltage offset entropy value corresponding to each typical fault in the typical fault subset corresponding to each line with a preset critical entropy value vector so as to determine the influence factor of the cascading faults of the alternating current and direct current power grid when a certain typical fault occurs in each line.
8. The system of claim 7, wherein the preset set of typical faults comprises: the main protection fault comprises a single-phase permanent short-circuit fault, a three-phase permanent short-circuit fault, a double-circuit line different-name phase-to-phase short-circuit fault and a double-circuit line different-name phase-to-phase short-circuit fault.
9. The system of claim 7, wherein the power flow entropy determination unit calculates the power flow entropy of the ac/dc power grid for any one line in the event of any one of the corresponding subset of typical faults by:
Figure FDA0003408324030000041
Figure FDA0003408324030000042
Figure FDA0003408324030000043
wherein, YPThe power flow entropy value of the alternating current and direct current power grid is obtained; zp(k) The load rate of the line is [ kb, (k +1) b]The line ratio, load factor sequence M ═ 0, b,2b … kb, … mb]Mb is 1, and b is a preset constant; i is the total number of lines; alpha is alphaiThe load rate of the ith line; piActive power, P, carried for the ith lineN,iRated active power of the ith line; l iskIndicates that the load factor is in the load interval [ kb, (k +1) b]Number of upper lines.
10. The system of claim 7, wherein the frequency offset entropy and voltage offset entropy determination unit calculates a wind turbine end frequency offset entropy value and a wind turbine end voltage offset entropy value of the wind turbine associated with any line when any of the corresponding subset of typical faults occurs and the line is cut off by using the following method, including:
Yf＝-(1-Zf)ln(1-Zf)，
Yu＝-(1-Zu)ln(1-Zu)，
Figure FDA0003408324030000051
Figure FDA0003408324030000052
Figure FDA0003408324030000053
Figure FDA0003408324030000054
wherein, YfAnd YuThe generator end frequency deviation entropy value and the generator end voltage of the wind power base respectively associated with the lineShifting an entropy value; zfAnd ZuThe off-grid ratios of the wind power bases associated with the line due to frequency offset and voltage offset are respectively calculated; pgfThe capacity of fan off-line caused by the wind power base with the machine end frequency deviation rate exceeding the preset frequency range; pguThe capacity of fan off-grid caused by the wind power base with the generator-end voltage deviation rate exceeding the preset voltage range; pgThe installed capacity of each wind power base; beta is aiThe machine end frequency deviation rate of the ith wind power base is obtained; f. ofiThe terminal frequency of the ith wind power base is the terminal frequency of the ith wind power base; f. ofNThe generator end rated frequency of the ith wind power base; gamma rayiThe generator terminal voltage deviation rate of the ith wind power base is obtained; u shapeiThe terminal voltage of the ith wind power base; u shapeNThe generator end rated voltage of the ith wind power base.
11. The system according to claim 7, wherein the influence factor determination unit compares the power flow entropy, the frequency shift entropy and the voltage shift entropy corresponding to any typical fault in any typical fault subset corresponding to any line with a preset critical entropy vector to determine the influence factor of the line causing cascading faults of the ac/dc power grid when the typical fault occurs, and includes:
the entropy vector construction module is used for constructing an entropy vector corresponding to any one of the typical fault subsets corresponding to any one line when any one of the typical faults occurs;
and the influence factor determining module is used for comparing the entropy vectors with corresponding entropy elements in a preset critical entropy vector one by one to determine result vectors, and determining influence factors causing cascading failure of the alternating current and direct current power grid when the line has the typical failure according to the result vectors.
12. The system according to claim 11, wherein the influencing factor determining module compares the entropy vector with corresponding elements in a preset critical entropy vector one by one to determine a result vector, and determines the influencing factor of the line, which causes the cascading failure of the ac/dc power grid when the typical failure occurs, according to the result vector, includes:
Figure FDA0003408324030000061
Figure FDA0003408324030000062
wherein, when x is p, YxThe entropy value of the power flow corresponding to the line when the typical fault occurs is obtained; y isxsetSetting a power flow entropy threshold value in a preset critical entropy vector; when x is f, YxShifting entropy value for the corresponding terminal frequency of the line when the typical fault occurs; y isxsetSetting a frequency offset entropy threshold value in a critical entropy value vector; when x is u, YxShifting entropy value for terminal voltage corresponding to the line when the typical fault occurs; y isxsetSetting a voltage offset entropy threshold value in a critical entropy value vector;
Figure FDA0003408324030000063
is the result vector if Fp1, indicating that the influencing factors comprise power flow transfer; if Ff1, indicating that the influencing factor comprises frequency offset; if FuA value of 1 indicates that the influencing factor comprises a voltage offset.
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