CN108390378B  MMCUPFC reliability modeling method  Google Patents
MMCUPFC reliability modeling method Download PDFInfo
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 CN108390378B CN108390378B CN201810381440.4A CN201810381440A CN108390378B CN 108390378 B CN108390378 B CN 108390378B CN 201810381440 A CN201810381440 A CN 201810381440A CN 108390378 B CN108390378 B CN 108390378B
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Classifications

 H—ELECTRICITY
 H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
 H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
 H02J3/00—Circuit arrangements for ac mains or ac distribution networks

 H—ELECTRICITY
 H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
 H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
 H02J3/00—Circuit arrangements for ac mains or ac distribution networks
 H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
 H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks

 H—ELECTRICITY
 H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
 H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
 H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
 H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
Abstract
The invention discloses an MMCUPFC reliability modeling method, which is characterized in that starting from the structural characteristics of the MMCUPFC, a UPFC component is divided into five subsystems, a Markov state space method is utilized to establish a state space model of each subsystem, an F & D method is utilized to carry out equivalence simplification, the logical relation of each subsystem is considered, a state enumeration method is utilized to establish a reliability model of the MMCUPFC, and reliability parameters are calculated. The method can be used for reliability evaluation of the power equipment with complex components, and has guiding significance for practical engineering application of the power equipment.
Description
Technical Field
The invention relates to a reliability modeling method for power equipment, in particular to a reliability modeling method for a Unified Power Flow Controller (UPFC) based on modular multilevel converter (MMC), namely an MMCUPFC reliability modeling method.
Background
The Unified Power Flow Controller (UPFC) integrates the control means of a plurality of FACTS devices, can effectively supplement the power flow control mode lacking in the old power grid, optimizes the power flow distribution and realizes the dynamic compensation of voltage, active power and reactive power. The modular multilevel converter (MMC) based UPFC (MMCUPFC for short) is suitable for the highvoltage and highcapacity field, and has a higher requirement on safe and reliable operation, so that the reliability of the UPFC is an important factor to be considered in practical engineering.
The traditional UPFC reliability model mainly has twostate, threestate and fourstate models, but has the following defects: firstly, a doubleloop structure of applying UPFC to a highvoltage largecapacity system is not considered; secondly, only the redundant structure and the converter bridge parallel structure of the converter valve of the submodule inside the MMC are considered, and the situation that the MMC is mutually standby is not considered; and thirdly, only the capability of realizing various running states of the UPFC is considered, the reasons of different working states caused by comprehensive analysis are not analyzed, and the accuracy of state transition rate calculation is influenced.
Disclosure of Invention
The invention provides a MMCUPFC reliability modeling method which is suitable for the field of highvoltage largecapacity power transmission and aims to solve the problems in the prior art.
The invention adopts the following technical scheme for solving the technical problems:
the MMCUPFC reliability modeling method is characterized in that: the MMCUPFC has a doubleloop structure, and the modeling method comprises the following steps:
step 1, dividing an assembly of the MMCUPFC into five subsystems according to the doubleloop structure characteristics of the MMCUPFC, wherein the five subsystems are as follows: a converter system S1, a parallel side transformer system S2, a series side transformer system S3, a DC bus and control system S4 and an offstation AC system S5;
step 2, reliability modeling is carried out on each subsystem by adopting a Markov state space method, and a state space model of each subsystem is established;
step 3, respectively carrying out equivalence simplification on the state space model of each subsystem to obtain the state probability P ' after equivalence simplification and the state transition rate a ' after equivalence simplification of each subsystem '_{IJ}And the equivalent postsimplification state transition rate a'_{IJ}Refers to the transition rate between state I and state J after the equivalence simplification;
step 4, enumerating seven running states of the UPFC by using a state enumeration method according to the logic relation among the subsystems;
step 5, utilizing the equivalent reduced state probability P 'and the equivalent reduced state transition rate a'_{IJ}And obtaining the reliability parameters of seven running states of the UPFC according to the logical relationship among the subsystems, and establishing an MMCUPFC reliability model according to the reliability parameters.
The MMCUPFC reliability modeling method is also characterized in that: the MMCUPFC has the characteristics of a doubleloop structure that: the three MMCs are connected to a direct current bus in a mutually standby mode, the serial connection side of the MMCUPFC independently operates to realize the function of the static synchronous serial compensator, and the parallel connection side of the MMCUPFC independently operates to realize the function of the static synchronous compensator.
The MMCUPFC reliability modeling method is also characterized in that: in step 2, a state space model of each subsystem is established according to the following process: considering the serialparallel relation and the running state of each subsystem component, establishing a state space model of each subsystem through permutation and combination, wherein each element in the state space model represents the running state of one subsystem; according to the fault rate and the repair rate of each subsystem component, respectively obtaining the beforeequivalence state probability P and the beforeequivalence state transition rate a of each subsystem_{ij}(ii) a The equivalence presimplification state transition rate a_{ij}Refers to the transition rate between state i and state j before the equalisation reduction.
The MMCUPFC reliability modeling method is also characterized in that: equivalent postsimplification state probability P ' and equivalent postsimplification state transition rate a ' in step 3 '_{IJ}Obtained as follows:
before equivalence simplification, the state probability P is a vector, and the vector P is: p ═ P (P)_{1},...p_{i}...,p_{n})^{T}，p_{i}Representing the state probability of the ith running state of the subsystem before the equivalence simplification, wherein i is more than or equal to 1 and less than or equal to n, and n represents the number of the running states of the subsystem before the equivalence simplification;
before equivalence simplification, the state transition rate A is a matrix, and the matrix A is as follows: a ═ a_{ij}]，1≤j≤n；
The equivalent simplified state probability P 'is a vector, and the vector P' is: p' ═ P (P)_{1}′,...p_{I}′...,p′_{m})^{T}，p_{1}The state probability of the Ith running state of the subsystem after the equivalence simplification is expressed, I is more than or equal to 1 and less than or equal to m, and m represents the running state number of the subsystem after the equivalence simplification;
the equivalent simplified state transition rate A 'is a matrix, and the matrix A' is: a '═ a'_{IJ}]，1≤J≤m；
The equivalent presimplification state probability P is obtained by the formula (1):
then: state transition frequency f before equivalence simplification_{ij}Comprises the following steps: f. of_{ij}＝a_{ij}p_{i} (2),
Equivalent state transition frequency f 'after simplification'_{IJ}Comprises the following steps:
state probability p of Ith running state of equivalent simplified subsystem_{i}' is:
state transition ratio a 'after equivalence'_{IJ}Obtained by simultaneous calculation of equations (3), (4) and (5):
f′_{IJ}＝a′_{IJ}p_{i}′ (5)。
the MMCUPFC reliability modeling method is also characterized in that: the seven running states of the UPFC refer to the full rated states of the UPFC, SSSC and STATCOM, the derating states of the UPFC, SSSC and STATCOM and the DOWN state of the DOWN.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention fully considers the doubleloop structure of the MMCUPFC subsystem in the field of highvoltage power transmission when dividing the MMCUPFC subsystem.
2. When the reliability model of the converter subsystem is established, the situation that the redundant structure of the converter valve of the submodule inside the MMC, the parallel structure of the converter bridge and the MMC are mutually standby is comprehensively considered.
3. The method flexibly uses a state space method and a state enumeration method, comprehensively, accurately and efficiently completes the reliability modeling of the MMCUPFC, and has reference value for the actual engineering application of the MMCUPFC in the highvoltage field.
Drawings
FIG. 1 is a schematic diagram of the partitioning of the doubleloop MMCUPFC structure and subsystems in the method of the present invention;
FIG. 2 is a logical relationship diagram of subsystems in the method of the present invention;
FIG. 3 is a state space model before equivalence of a converter subsystem S1 in the method of the present invention
FIG. 4 is a state space model after the converter subsystem S1 is equivalent in the method of the present invention;
Detailed Description
In the MMCUPFC reliability modeling method of the embodiment, the MMCUPFC has a doubleloop structure, and the modeling method comprises the following steps:
step 1, dividing an assembly of the MMCUPFC into five subsystems according to the doubleloop structure characteristics of the MMCUPFC, wherein the five subsystems are respectively as follows: three groups of converter systems S1, parallel side transformer system S2, series side transformer system S3, dc bus and control system S4 and station external ac system S5, which are backup to each other, as shown in fig. 1 and 2.
The MMCUPFC has the characteristics of a doubleloop structure that: three MMCs are mutually standby and are directly connected to a direct current bus through a changeover switch without connecting a direct current support capacitor; when the system normally operates, one MMC is connected with an alternating current bus through a parallel transformer, and two MMCs are respectively connected with a doublecircuit line through a series transformer; when the serial side of the MMCUPFC operates independently, the function of a Static Synchronous Series Compensator (SSSC) is realized, and when the parallel side of the MMCUPFC operates independently, the function of the static synchronous compensator (STATCOM) is realized; the MMC is composed of a plurality of converter valve submodules, the converter valve submodules are connected into converter bridges in series, and if alternating current sides of two groups of converter bridges are connected in parallel, the MMC realizes derating operation.
Step 2, respectively carrying out reliability modeling on each subsystem by adopting a Markov state space method, establishing a state space model of each subsystem, specifically, considering the seriesparallel relation and the running state of each subsystem component, and establishing the state space model of each subsystem by permutation and combination, wherein each element in the state space model represents the running state of one subsystem; respectively obtaining each subsystem according to the failure rate and the repair rate of each subsystem componentBeforeequatingsimplification state probability P and beforeequatingsimplification state transition rate a_{ij}Equivalence State transition Rate a before simplification_{ij}Refers to the transition rate between state i and state j before the equalisation reduction.
Step 3, respectively carrying out equivalence simplification on the state space models of the subsystems, merging the same running states to obtain the equivalence simplified state probability P ' and the equivalence simplified state transition rate a ' of the subsystems '_{IJ}Equivalence ratio of postsimplification State transition ratio a'_{IJ}Refers to the transition rate between state I and state J after the equivalent simplification.
And 4, establishing a logic diagram as shown in fig. 2 according to the logic relationship among the subsystems, and enumerating seven operating states of the UPFC by using a state enumeration method, wherein the seven operating states of the UPFC refer to the full state of the UPFC, the SSSC and the STATCOM, the derating state of the UPFC, the SSSC and the STATCOM, and the DOWN state of the outage state.
Step 5, utilizing the equivalent simplified state probability P 'and the equivalent simplified state transition rate a'_{IJ}And obtaining the reliability parameters of seven running states of the UPFC according to the logical relation among the subsystems, and establishing an MMCUPFC reliability model according to the reliability parameters.
In specific implementation, the equivalent postsimplification state probability P 'and the equivalent postsimplification state transition rate a'_{IJ}Obtained as follows:
before equivalence simplification, the state probability P is a vector, and the vector P is: p ═ P (P)_{1},...p_{i}...,p_{n})^{T}，p_{i}Representing the state probability of the ith running state of the subsystem before the equivalence simplification, wherein i is more than or equal to 1 and less than or equal to n, and n represents the number of the running states of the subsystem before the equivalence simplification;
before equivalence simplification, the state transition rate A is a matrix, and the matrix A is as follows: a ═ a_{ij}]，1≤j≤n；
The equivalent simplified state probability P 'is a vector, and the vector P' is: p' ═ P (P)_{1}′,...p_{I}′...,p′_{m})^{T}，p_{1}The state probability of the Ith running state of the subsystem after the equivalence simplification is expressed, I is more than or equal to 1 and less than or equal to m, and m represents the running state of the subsystem after the equivalence simplificationCounting;
the equivalent simplified state transition rate A 'is a matrix, and the matrix A' is: a '═ a'_{IJ}]；1≤J≤m；
The equivalent presimplification state probability P is obtained by the formula (1):
then: state transition frequency f before equivalence simplification_{ij}Comprises the following steps: f. of_{ij}＝a_{ij}p_{i} (2),
Equivalent state transition frequency f 'after simplification'_{IJ}Comprises the following steps:
state probability p of Ith running state of equivalent simplified subsystem_{i}' is:
state transition ratio a 'after equivalence'_{IJ}Obtained by simultaneous calculation of equations (3), (4) and (5):
f′_{IJ}＝a′_{IJ}p_{i}′ (5)。
in the specific implementation, the establishment of the state space model of each subsystem by adopting the Markov state space method is carried out as follows:
establishing a state space model of the converter system S1 is shown in fig. 3: numbering the three groups of converters as a converter C1, a converter C2 and a converter C3, and assuming that the converter C1 is connected with the parallel side first; each converter has three operation states of full rating (1), derating (0.5) and stopping (0); lambda and mu respectively represent failure rate and repair rate; by "1", "0.5^{+}”、“0.25^{+}”、“0.5^{}”、“0.25^{}"and" 0 "means that converter system S1 meets the requirements for full, derated, and DOWN states for three functions, UPFC, SSSC, and STATCOM. The equivalent simplification of the state space model of FIG. 3 results in the equivalent of subsystem S1Value state space model, as shown in fig. 4.
The parallel side transformer system S2, the series side transformer system S3, and the dc bus and control system S4 have different internal components, but have two operating states, namely normal (1) and shutdown (0).
The offsite AC system S5 can be divided into an intraarea part and an extraarea part according to different influence degrees, wherein the intraarea part is an area between two buses accessed by the UPFC and comprises the two buses, and the extraarea part is an AC power grid part except the intraarea part.
For outofrange faults, the effects of unbalanced voltages, overvoltages, undervoltages and overcurrents that may be caused by a UPFC, whether transient or permanent, can only cause temporary blocking of some or all of the converters of the UPFC to the most severe extent. And after the outside fault is removed, the system recovers to normal operation, the UPFC can be put into operation again in a very short time, the time required in the whole process is in the second level, and the reliability of the UPFC is basically not influenced.
For the internal fault, if the two buses have permanent faults, the whole doublecircuit UPFC is stopped; if the singlecircuit transmission line has a fault, the series side of the UPFC is changed into singlecircuit operation, and the derating of the UPFC is performed by half of the normal capacity. Therefore, the offsite traffic system S5 has three operating states: normal (1), derated (0.5) and shutdown (0).
The MMCUPFC function and each subsystem state combination are shown in Table 1:
table 1: UPFC sevenstate function table
As shown in table 1: in the converter system S1, the right side of the derating state 0.5 indicates, for the parallel side, a UPFC derating state caused by derating of the parallel side converter, and for the series side, a UPFC derating state caused by derating of the series side converter; 1/0 indicates a normal or shut down condition; 1/0.5 indicates a normal or derated state.
Table 2: MMCUPFC sevenstate probability table
And calculating to obtain seven reliability parameters of the UPFC in the running state according to the equivalent state probability of each subsystem and the state combination relation of each subsystem, wherein the table 2 shows the seven state probabilities of the MMCUPFC.
Claims (2)
1. An MMCUPFC reliability modeling method is characterized in that: the MMCUPFC has a doubleloop structure, and the modeling method comprises the following steps:
step 1, dividing an assembly of the MMCUPFC into five subsystems according to the doubleloop structure characteristics of the MMCUPFC, wherein the five subsystems are as follows: a converter system S1, a parallel side transformer system S2, a series side transformer system S3, a DC bus and control system S4 and an offstation AC system S5;
the MMCUPFC has the characteristics of a doubleloop structure that: three MMCs are connected to a direct current bus in a mutually standby mode, the function of a static synchronous series compensator is realized when the serial sides of the MMCUPFC operate independently, and the function of the static synchronous compensator is realized when the parallel sides of the MMCUPFC operate independently;
step 2, reliability modeling is respectively carried out on each subsystem by adopting a Markov state space method, and a state space model of each subsystem is established according to the following processes: considering the serialparallel relation and the running state of each subsystem component, establishing a state space model of each subsystem through permutation and combination, wherein each element in the state space model represents the running state of one subsystem; according to the fault rate and the repair rate of each subsystem component, respectively obtaining the beforeequivalence state probability P and the beforeequivalence state transition rate a of each subsystem_{ij}(ii) a The equivalence presimplification state transition rate a_{ij}Refers to the transition rate between state i and state j before isoid reduction;
step 3, respectively carrying out equivalence simplification on the state space model of each subsystem to obtain the state probability P ' after equivalence simplification and the state transition rate a ' after equivalence simplification of each subsystem '_{IJ}And the equivalent postsimplification state transition rate a'_{IJ}Refers to the transition rate between state I and state J after the equivalence simplification;
equivalent postsimplification state probability P 'and equivalent postsimplification state transition rate a'_{IJ}Obtained as follows:
before equivalence simplification, the state probability P is a vector, and the vector P is: p ═ P (P)_{1},...p_{i}...,p_{n})^{T}，p_{i}Representing the state probability of the ith running state of the subsystem before the equivalence simplification, wherein i is more than or equal to 1 and less than or equal to n, and n represents the number of the running states of the subsystem before the equivalence simplification;
before equivalence simplification, the state transition rate A is a matrix, and the matrix A is as follows: a ═ a_{ij}]，1≤j≤n；
The equivalent simplified state probability P 'is a vector, and the vector P' is: p '═ P'_{1},...p′_{I}...,p′_{m})^{T}，p_{I}The state probability of the Ith running state of the subsystem after the equivalence simplification is expressed, I is more than or equal to 1 and less than or equal to m, and m represents the running state number of the subsystem after the equivalence simplification;
the equivalent simplified state transition rate A 'is a matrix, and the matrix A' is: a '═ a'_{IJ}]，1≤J≤m；
The equivalent presimplification state probability P is obtained by the formula (1):
then: state transition frequency f before equivalence simplification_{ij}Comprises the following steps: f. of_{ij}＝a_{ij}p_{i} (2)
Equivalent state transition frequency f 'after simplification'_{IJ}Comprises the following steps:
state probability p of Ith running state of equivalent simplified subsystem_{I}' is:
state transition ratio a 'after equivalence'_{IJ}Obtained by simultaneous calculation of equations (3), (4) and (5):
f′_{IJ}＝a′_{IJ}p_{I}′ (5)
step 4, enumerating seven running states of the UPFC by using a state enumeration method according to the logic relation among the subsystems;
step 5, utilizing the equivalent reduced state probability P 'and the equivalent reduced state transition rate a'_{IJ}And obtaining the reliability parameters of seven running states of the UPFC according to the logical relationship among the subsystems, and establishing an MMCUPFC reliability model according to the reliability parameters.
2. The MMCUPFC reliability modeling method of claim 1, wherein: the seven running states of the UPFC refer to the full rated states of the UPFC, SSSC and STATCOM, the derating states of the UPFC, SSSC and STATCOM and the DOWN state of the DOWN.
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