CN108390378B - MMC-UPFC reliability modeling method - Google Patents

MMC-UPFC reliability modeling method Download PDF

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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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upfc
simplification
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mmc
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CN108390378A (en
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韩平平
胡骞
夏雨
张宇
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Hefei University of Technology
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

Abstract

The invention discloses an MMC-UPFC reliability modeling method, which is characterized in that starting from the structural characteristics of the MMC-UPFC, 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 MMC-UPFC, 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

MMC-UPFC reliability modeling method
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 multi-level converter (MMC), namely an MMC-UPFC 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 multi-level converter (MMC) -based UPFC (MMC-UPFC for short) is suitable for the high-voltage and high-capacity 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 two-state, three-state and four-state models, but has the following defects: firstly, a double-loop structure of applying UPFC to a high-voltage large-capacity 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 MMC-UPFC reliability modeling method which is suitable for the field of high-voltage large-capacity 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 MMC-UPFC reliability modeling method is characterized in that: the MMC-UPFC has a double-loop structure, and the modeling method comprises the following steps:
step 1, dividing an assembly of the MMC-UPFC into five subsystems according to the double-loop structure characteristics of the MMC-UPFC, 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 off-station 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 'IJAnd the equivalent post-simplification state transition rate a'IJRefers 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'IJAnd obtaining the reliability parameters of seven running states of the UPFC according to the logical relationship among the subsystems, and establishing an MMC-UPFC reliability model according to the reliability parameters.
The MMC-UPFC reliability modeling method is also characterized in that: the MMC-UPFC has the characteristics of a double-loop structure that: the three MMCs are connected to a direct current bus in a mutually standby mode, the serial connection side of the MMC-UPFC independently operates to realize the function of the static synchronous serial compensator, and the parallel connection side of the MMC-UPFC independently operates to realize the function of the static synchronous compensator.
The MMC-UPFC 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 serial-parallel 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 before-equivalence state probability P and the before-equivalence state transition rate a of each subsystemij(ii) a The equivalence pre-simplification state transition rate aijRefers to the transition rate between state i and state j before the equalisation reduction.
The MMC-UPFC reliability modeling method is also characterized in that: equivalent post-simplification state probability P ' and equivalent post-simplification state transition rate a ' in step 3 'IJObtained as follows:
before equivalence simplification, the state probability P is a vector, and the vector P is: p ═ P (P)1,...pi...,pn)T,piRepresenting 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 ═ aij],1≤j≤n;
The equivalent simplified state probability P 'is a vector, and the vector P' is: p' ═ P (P)1′,...pI′...,p′m)T,p1The state probability of the I-th 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 pre-simplification state probability P is obtained by the formula (1):
then: state transition frequency f before equivalence simplificationijComprises the following steps: f. ofij=aijpi (2),
Equivalent state transition frequency f 'after simplification'IJComprises the following steps:
state probability p of I-th running state of equivalent simplified subsystemi' is:
state transition ratio a 'after equivalence'IJObtained by simultaneous calculation of equations (3), (4) and (5):
f′IJ=a′IJpi′ (5)。
the MMC-UPFC 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 double-loop structure of the MMC-UPFC subsystem in the field of high-voltage power transmission when dividing the MMC-UPFC 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 MMC-UPFC, and has reference value for the actual engineering application of the MMC-UPFC in the high-voltage field.
Drawings
FIG. 1 is a schematic diagram of the partitioning of the double-loop MMC-UPFC 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 MMC-UPFC reliability modeling method of the embodiment, the MMC-UPFC has a double-loop structure, and the modeling method comprises the following steps:
step 1, dividing an assembly of the MMC-UPFC into five subsystems according to the double-loop structure characteristics of the MMC-UPFC, 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 MMC-UPFC has the characteristics of a double-loop structure that: three MMCs are mutually standby and are directly connected to a direct current bus through a change-over 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 double-circuit line through a series transformer; when the serial side of the MMC-UPFC operates independently, the function of a Static Synchronous Series Compensator (SSSC) is realized, and when the parallel side of the MMC-UPFC operates independently, the function of the static synchronous compensator (STATCOM) is realized; the MMC is composed of a plurality of converter valve sub-modules, the converter valve sub-modules 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 series-parallel 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 componentBefore-equating-simplification state probability P and before-equating-simplification state transition rate aijEquivalence State transition Rate a before simplificationijRefers 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 'IJEquivalence ratio of post-simplification State transition ratio a'IJRefers 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'IJAnd obtaining the reliability parameters of seven running states of the UPFC according to the logical relation among the subsystems, and establishing an MMC-UPFC reliability model according to the reliability parameters.
In specific implementation, the equivalent post-simplification state probability P 'and the equivalent post-simplification state transition rate a'IJObtained as follows:
before equivalence simplification, the state probability P is a vector, and the vector P is: p ═ P (P)1,...pi...,pn)T,piRepresenting 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 ═ aij],1≤j≤n;
The equivalent simplified state probability P 'is a vector, and the vector P' is: p' ═ P (P)1′,...pI′...,p′m)T,p1The state probability of the I-th 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 pre-simplification state probability P is obtained by the formula (1):
then: state transition frequency f before equivalence simplificationijComprises the following steps: f. ofij=aijpi (2),
Equivalent state transition frequency f 'after simplification'IJComprises the following steps:
state probability p of I-th running state of equivalent simplified subsystemi' is:
state transition ratio a 'after equivalence'IJObtained by simultaneous calculation of equations (3), (4) and (5):
f′IJ=a′IJpi′ (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 off-site AC system S5 can be divided into an intra-area part and an extra-area part according to different influence degrees, wherein the intra-area part is an area between two buses accessed by the UPFC and comprises the two buses, and the extra-area part is an AC power grid part except the intra-area part.
For out-of-range faults, the effects of unbalanced voltages, over-voltages, under-voltages and over-currents 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 double-circuit UPFC is stopped; if the single-circuit transmission line has a fault, the series side of the UPFC is changed into single-circuit operation, and the derating of the UPFC is performed by half of the normal capacity. Therefore, the off-site traffic system S5 has three operating states: normal (1), derated (0.5) and shutdown (0).
The MMC-UPFC function and each subsystem state combination are shown in Table 1:
table 1: UPFC seven-state 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: MMC-UPFC seven-state 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 MMC-UPFC.

Claims (2)

1. An MMC-UPFC reliability modeling method is characterized in that: the MMC-UPFC has a double-loop structure, and the modeling method comprises the following steps:
step 1, dividing an assembly of the MMC-UPFC into five subsystems according to the double-loop structure characteristics of the MMC-UPFC, 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 off-station AC system S5;
the MMC-UPFC has the characteristics of a double-loop 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 MMC-UPFC operate independently, and the function of the static synchronous compensator is realized when the parallel sides of the MMC-UPFC 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 serial-parallel 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 before-equivalence state probability P and the before-equivalence state transition rate a of each subsystemij(ii) a The equivalence pre-simplification state transition rate aijRefers 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 'IJAnd the equivalent post-simplification state transition rate a'IJRefers to the transition rate between state I and state J after the equivalence simplification;
equivalent post-simplification state probability P 'and equivalent post-simplification state transition rate a'IJObtained as follows:
before equivalence simplification, the state probability P is a vector, and the vector P is: p ═ P (P)1,...pi...,pn)T,piRepresenting 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 ═ aij],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,pIThe state probability of the I-th 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 pre-simplification state probability P is obtained by the formula (1):
then: state transition frequency f before equivalence simplificationijComprises the following steps: f. ofij=aijpi (2)
Equivalent state transition frequency f 'after simplification'IJComprises the following steps:
state probability p of I-th running state of equivalent simplified subsystemI' is:
state transition ratio a 'after equivalence'IJObtained by simultaneous calculation of equations (3), (4) and (5):
f′IJ=a′IJpI′ (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'IJAnd obtaining the reliability parameters of seven running states of the UPFC according to the logical relationship among the subsystems, and establishing an MMC-UPFC reliability model according to the reliability parameters.
2. The MMC-UPFC 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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