CN113595051A - Stepped addressing and multi-objective optimization constant volume method for current power flow controller - Google Patents

Stepped addressing and multi-objective optimization constant volume method for current power flow controller Download PDF

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CN113595051A
CN113595051A CN202010366782.6A CN202010366782A CN113595051A CN 113595051 A CN113595051 A CN 113595051A CN 202010366782 A CN202010366782 A CN 202010366782A CN 113595051 A CN113595051 A CN 113595051A
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cfc
line
power flow
current
converter station
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王谱宇
甄浩
王松
杨伟
卜京
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Nanjing University of Science and Technology
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Nanjing University of Science and Technology
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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
    • H02J1/00—Circuit arrangements for dc mains or dc 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
    • H02J3/008—Circuit arrangements for ac mains or ac distribution networks involving trading of energy or energy transmission rights
    • 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

The invention discloses a method for the stepwise addressing and the multi-objective optimization constant volume of a current power flow controller, which comprises the steps of inputting initial data of a power grid; performing initial load flow calculation on the direct current power grid; establishing a comprehensive index system for the direct-current power grid, wherein the comprehensive index system is used for considering the direct-current line load flow performance and the direct-current output voltage performance of the converter station; screening all lines according to the DC CFC site selection principle to obtain a target line set gamma meeting the installation requirement; selecting the main DC CFC address under the normal operation condition; selecting the standby DC CFC site under the N-1 operation condition; taking economic and safety indexes as comprehensive evaluation indexes, establishing a DC CFC capacity multi-target optimization function, and converting multi-target optimization into single-target optimization by adopting a linear combination optimization method with conversion weighting; establishing an optimization constraint condition by using the constraint of a conventional power system and the constraint of the internal power of the DC CFC; and (3) taking the capacity of the DC CFC main control line/auxiliary control line converter as a variable to be optimized, and optimizing by using a genetic algorithm to obtain the optimal capacity. The invention has strong practicability and is scientific and reasonable.

Description

Stepped addressing and multi-objective optimization constant volume method for current power flow controller
Technical Field
The invention relates to a current power flow controller, in particular to a stepwise addressing and multi-objective optimization constant volume method for the current power flow controller.
Background
The current flow controller (DC CFC) has strong power flow regulation and control capability, simple structure and the potential of expanding multiple degrees of freedom, and provides possibility for further development of a direct current power grid. As a voltage-changing type direct current power flow controller, the topological structure of the DC CFC is different from that of the traditional DC/DC converter type and auxiliary voltage source type power flow controllers. The device has a simple structure, needs few power electronic devices, only carries out directional and quantitative transmission of the tidal current between lines without energy exchange with an external power grid, does not need to bear the high voltage of a system level, has the potential of expanding dual-control freedom degree, and has good application prospect.
Most of the existing researches for DC CFC site selection and volume measurement are based on sensitivity or intelligent algorithm optimization, but in practical engineering application, the site selection work of the DC CFC is often more focused on improving the system power transmission capacity and solving the line overload problem influencing the power transmission safety by utilizing the power flow regulation and control capacity of the DC CFC, so that the constraint of the DC CFC site selection by using sensitivity indexes and economic indexes is unreasonable. Based on the method, a DC CFC step-by-step site selection method based on comprehensive safety indexes is provided, and a DC CFC multi-objective optimization constant volume strategy giving consideration to both economy and safety is provided on the basis.
Disclosure of Invention
The invention aims to provide a method for stepwise addressing and multi-objective optimization constant volume of a current and power flow controller.
The technical solution for realizing the purpose of the invention is as follows: a method for stepwise site selection and multi-objective optimization constant volume of a current and power flow controller comprises the following steps:
step 1, inputting initial data of a power grid;
step 2, performing initial load flow calculation on the direct current network;
step 3, establishing a comprehensive index system for the direct-current power grid, wherein the comprehensive index system is used for considering the direct-current line load flow performance and the direct-current output voltage performance of the converter station;
step 4, screening all lines according to the DC CFC site selection principle to obtain a target line set gamma meeting the installation requirement;
step 5, selecting the main DC CFC site under the normal operation condition;
6, selecting the standby DC CFC address under the operation condition of N-1;
step 7, taking economic and safety indexes as comprehensive evaluation indexes, establishing a DC CFC capacity multi-target optimization function, and converting multi-target optimization into single-target optimization by adopting a linear combination optimization method with conversion weighting;
step 8, establishing an optimized constraint condition by using the constraint of a conventional power system and the constraint of the internal power of the DC CFC;
and 9, taking the capacity of the DC CFC main control circuit/auxiliary control circuit converter as a variable to be optimized, optimizing by using a genetic algorithm to obtain the optimal capacity, and completing volume fixing.
Compared with the prior art, the invention has the following remarkable advantages: the DC CFC site selection principle is provided; a comprehensive index system considering the power flow performance of a direct-current line and the direct-current output voltage performance of a converter station is established for a direct-current power grid, a scientific and effective DC CFC site selection strategy is established by combining a DC CFC site selection principle and the comprehensive index system of the direct-current power grid, and the directional allocation effect of the DC CFC on the power flow of the line is better exerted; provides a DC CFC multi-target optimization constant volume method, and improves the construction economy of the DC CFC.
Drawings
Figure 1 is a diagram of a DC CFC topology.
Fig. 2 is a graph of a sine conversion function.
Fig. 3 is a five-terminal dc grid topology diagram in an embodiment of the invention.
Fig. 4 is a five-terminal DC power grid topology diagram after two DC CFCs are installed in the embodiment of the present invention.
Fig. 5 is a graph of iterative convergence of objective function values in an embodiment of the present invention.
FIG. 6 is a flow chart of stepwise addressing and multi-objective optimization constant volume of a current and power flow controller
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings.
Step 1, inputting power grid initial data, including types of nodes of a direct-current power grid, P node injection active power corresponding to a power control station, V node reference voltage corresponding to a voltage control station and branch resistances;
without loss of generality, assume that a dc grid has N nodes (1,2, … i … j … k … p … q … N), b branches, where node N operates in a constant dc voltage mode and the other nodes operate in a constant active power mode. Suppose that the DC CFC is installed on a branch ij and a branch ik connected with a node i, wherein the branch ij is a main control line, the branch ik is an auxiliary control line, and the equivalent direct current voltage introduced by the DC CFC on the main (auxiliary) control line is eij(eik) And nodes p and q represent any node.
Step 2, performing initial load flow calculation on the direct current network;
the grid does not contain the DC CFC at this time. If the current injected into the direct current power grid is positive, the current flowing through any node p can be expressed as formula (1), the relation between the node active power and the current and voltage can be expressed as formula (2), and the active power injected into the direct current power grid by the node p is expressed as formula (3):
Figure BDA0002476956600000031
Pp＝IpUp (2)
Pp＝Pc,dcp+Pgp-Pdp (3)
in the formula IpIs the current flowing through node p; u shapep、UqThe voltages of nodes p, q; gpqIs the line conductance between nodes p, q; ppInjection power for node P, Pc,dcpActive power injected into the direct current power grid for the converter station; pgpOutputting power for the node p equivalent direct current source; pdpThe node p is equivalent to the absorbed power of the dc load. The formulas (1-3) form a basic direct current power grid load flow model. Writing a DC power grid power flow equation according to the known PpAnd UpPerforming Newton-Raphson power flow iteration to obtain the solution of DCAnd (5) power flow of a power grid.
Step 3, establishing a comprehensive index system for the direct-current power grid, wherein the comprehensive index system is used for considering the direct-current line load flow performance and the direct-current output voltage performance of the converter station;
1) and (4) a DC line power flow performance index.
When the safety verification of the direct current network is carried out, the distribution of the original system is greatly influenced, the power transmitted on each line is greatly changed, and a heavy load or even an overload line occurs, so that the safe operation of the system is influenced. And (3) providing a direct-current line tide performance index formula (4) and a system tide performance index formula (5) to quantitatively describe the tide performance of the power grid:
Figure BDA0002476956600000032
Figure BDA0002476956600000033
in formulae (4) to (5): i isP-pqIs a branch pq power flow performance index, IPIs a system tidal current performance index; ppqIs the active power flow on branch pq;
Figure BDA0002476956600000034
is the rated active power flow of the branch pq; n is an exponential coefficient and its value is a positive integer, usually taken as 1; alpha is a line set; omegapqIs a weighting factor reflecting the importance of the branch. Thus defined IP-pqThe actual power flow is intuitively compared with the power flow limit, the margin between the actual power flow and the limit power flow can be reflected, and the larger the value of the margin is, the closer the power flow on the line is to the power flow limit value of the system. Thereby containing information of the blocking of the transmission line. When n is 1, IP-pqHas a normal value range of (0, 0.5)]A value higher than 0.5 means that the line is in an overload state.
Through IP-pqAnd IPThe value of (d) can reflect the static safety state of the line pq and the line in the whole direct current power grid.
2) DC output voltage performance index of converter station
Defining a direct-current output voltage performance index of a direct-current power grid converter station, wherein the index is used for measuring the deviation degree of an outlet voltage operating point of the converter station and a reference operating point thereof:
Figure BDA0002476956600000041
Figure BDA0002476956600000042
Figure BDA0002476956600000043
Figure BDA0002476956600000044
in formulae (6) to (9): i isU-pIs a p DC output voltage performance index, I, of the converter stationUIs a system voltage performance indicator; u shapepIs the node p outlet voltage; m is an exponential coefficient and its value is a positive integer, usually taken as 1; beta is a converter station set; omegapIs a weight factor reflecting the importance of the converter station;
Figure BDA0002476956600000045
the upper and lower limits of the outlet voltage of the converter station p.
The voltage performance indexes at two ends of the line pq can be obtained by calculating the performance indexes of the outlet voltages of the p converter station and the q converter station, wherein the formula (10) is as follows:
Figure BDA0002476956600000046
IU-pqthe offset of the voltage on two sides of the line pq is reflected, and is one index for measuring the health condition of the line pq. I isUComprehensively reflects the degree of deviation of the outlet voltage of each converter station of the direct current power grid from a rated valueThe larger the deviation of the outlet voltage of the power grid converter station is, the larger the deviation is, and the existence of the index coefficient causes the performance index to be rapidly increased when the voltage is lower, and the direct current power grid voltage performance is reflected to be poor. When m is 1, IU-pqHas a normal value range of [0,1 ]]A value higher than 1 means that the dc output voltage offset of at least 1 converter station on both sides of the line pq exceeds the limit value.
3) Comprehensive safety margin index
The health condition of the line pq can be obtained by comprehensively considering the active power flow performance of the line pq and the outlet voltage performance of the converter stations on two sides of the line pq, and the health condition is used as a Comprehensive safety standard (CI) formula (11) for CFC installation requirements.
Figure BDA0002476956600000047
Using formula (11) as a comprehensive measure: CIpqAnd CIsumRespectively representing the comprehensive safety margin indexes of the line pq and the whole system; eta1、η2、μ1、μ2The parameter weights are respectively represented, and the importance degree of the parameters is reflected.
Step 4, screening all lines according to the DC CFC site selection principle to obtain a target line set gamma meeting the installation requirement;
the DC CFC is a multi-terminal topology, and has a plurality of full-bridge converters installed on the circuit, so the addressing work is more complicated. The topological structure and the working principle are considered, and the following DC CFC addressing principle is provided:
1) the DC CFC is required to be arranged in a direct current looped network;
2) when the line power flow can be completely controlled only by the converter station on the transmission line, the DC CFC does not need to be installed;
3) the converter station at the DC CFC installation node is provided with at least two outgoing lines, and the DC CFC controls the power flow of at least two branches at the same time;
4) the DC CFC auxiliary control line must have sufficient capacity margin;
and selecting the line set gamma meeting the installation requirement from the line set alpha according to the site selection principle.
Step 5, selecting the main DC CFC site under the normal operation condition;
1) under the normal operation condition of the system, the comprehensive performance index CI of the circuit is utilizedpqSorting each line in the set gamma, selecting CIpqThe line with the highest value is used as a main control line of the main DC CFC;
2) selecting CI in the determined lines connected with the converter stations at two ends of the main control linepqThe lowest value line is used as an auxiliary control line of the main DC CFC;
6, selecting the standby DC CFC address under the operation condition of N-1;
1) n-1 fault analysis is carried out on all lines in the power grid, and the performance index I of the lines can be ensured by controlling the converter station and the DC CFC after the faultsP-pqAnd IU-pqThe fault set that all meet the system operation requirements is recorded as fault set delta1And other faults are recorded as a fault set delta2. Determination of delta2If the current set is an empty set, if so, ending the step 6, otherwise, entering the next step;
2) finding delta2System safety index CI under fault of each linesumUsing CIsumFor fault set delta2The line faults in the system are sorted according to severity, and a plurality of more serious line fault conditions (such as simple power grid or delta) are selected2And (3) less internal elements, and all line fault conditions can be selected for calculation): calculating CI of lines in fault condition in set gamma according to importance degree of linespqA weighted average;
3) selecting CIpqThe line with the highest weighted average value is used as the main control line of the standby DC CFC, and the CI which is positioned in the set gamma is selected from the lines connected by the converter stations at the two ends of the determined main control linepqThe line with the lowest weighted average value is used as the DC CFC auxiliary control line;
4) judging whether the DC CFC still needs to be installed, if so, returning to the step 6-3) to select CIpqThe line with the second highest weighted average value is used as the main control line of the standby DC CFC and finishes the step, if not, the step is finished;
step 7, taking economic and safety indexes as comprehensive evaluation indexes, establishing a DC CFC capacity multi-target optimization function, and converting multi-target optimization into single-target optimization by adopting a linear combination optimization method with conversion weighting;
1) objective function
Figure BDA0002476956600000061
Figure BDA0002476956600000062
Figure BDA0002476956600000063
In formulae (12) to (13), IPIs a DC line power flow performance index; ppqIs the active power flow on branch pq;
Figure BDA0002476956600000064
is the nominal delivery capacity of the branch pq; n is an exponential coefficient and its value is a positive integer; alpha is a converter station set; omegapqIs a weight factor reflecting the importance of the branch; i isUIs the performance index of the direct current output voltage of the converter station; u shapepIs the dc outlet voltage of the converter station pddc; m is an exponential coefficient and its value is a positive integer; beta is a converter station set; omegapIs a weight factor reflecting the importance of the converter station;
in the formula (14), f (S) is a DC CFC construction cost function, wherein a, b and c are price constants, a is more than 1, b is more than 1, c is more than 1, and a is more than b and less than c; s1、S2For DC CFC main control (auxiliary control) line converter capacity, nyIs the economic operation life of the DC CFC.
2) Converting multi-objective optimization into single-objective optimization
The above-mentioned consideration of electric power system operation security and economic nature index forms multiobjective optimization functional formula (15):
Figure BDA0002476956600000065
for the multi-objective optimization function, as many Pareto optimal solution sets as possible can be found by adopting an NSGA-2 algorithm, but the satisfactory solution is difficult to decide from the Pareto optimal solution sets. Thus, the conversion weighting method is adopted to optimize the function f by the partial target using the sine conversion function in FIG. 2p(X) conversion to a dimensionless and equal-magnitude objective function
Figure BDA0002476956600000066
Then using the converted partial objective function and the weighting factor omegapForming a new unified target function:
Figure BDA0002476956600000067
in the formula (16), ωpOptimizing weight coefficients for multiple objectives, where ω1、ω2The method is the weight of the safety index, and reflects the attention degree, omega, of the requirement on the operation safety of the direct current power grid3The method is the weight occupied by the economic indexes, and reflects the attention degree of the power grid operation economic requirement. Note here that f in the sinusoidal transfer functionpUpper limit of (X) < beta >pThe value of (a) is not necessarily selected according to physical limits and can be further reduced according to optimization objectives.
Step 8, establishing an optimized constraint condition by using the constraint of a conventional power system and the constraint of the internal power of the DC CFC;
Figure BDA0002476956600000071
the meanings of the expressions in the formula (17) have been specifically described in step 2.
Figure BDA0002476956600000072
Figure BDA0002476956600000073
In the formulae (18) to (19), Δ I is a current error term, IijrefA current command value set for the line ij; delta PbbiAdditional injection power, δ P, introduced for DC CFC at node iijAdditional injection power, deltaP, introduced on line ij close to node i for the DC CFCikThe same process is carried out;
Figure BDA0002476956600000074
Figure BDA0002476956600000075
in formula (20), Udcp、PdcpRespectively injecting the active power of the direct current power grid into the voltage p and the change point of any node of the direct current power grid; e in formula (21)ij、eikThe equivalent direct current voltage is introduced into the DC CFC main control and auxiliary control circuit.
And 9, taking the DC CFC main control circuit/auxiliary control circuit converter capacity and the main control circuit current instruction value as variables to be optimized, optimizing by using a genetic algorithm to obtain the optimal capacity, and completing constant volume.
The method adopts comprehensive safety indexes including a direct current line tide performance index and a converter station direct current output voltage performance index to perform safety evaluation on the operation state of a system line, and determines the optimal installation position of the DC CFC by combining a power grid transmission problem link screened under an N-1 working condition; on the basis, the DC CFC multi-target optimization constant volume taking the economy and the safety into consideration is carried out, and the method is strong in practicability, scientific and reasonable.
Examples
In order to verify the effectiveness of the scheme of the invention, the effectiveness of the method is verified by taking a direct current power grid formed by adding branches L13 and L15 to a Zhoushan five-terminal direct current system as an example, and the voltage level of the power grid is 400 kV.
Fig. 3 shows the grid topology. In the figure, 1,2,3,4 and 5 are numbers of converter stations, the number of the AC-DC converter stations (nodes) is 5, the node 1 of the converter station is a V node, and the rest nodes are P nodes.
The parameters of the dc grid system before installation of the CFC are shown in table 1.
The experimental environment is as follows: the number of the AC-DC converter stations (nodes) is 5, the converter station node 1 is a V node, the other nodes are P nodes, the voltage value of the V node is 400 multiplied by 1e 3V, P, the net injection power value is shown in table 1, and the DC line parameters between the nodes are shown in table 1;
TABLE 1 original DC network control mode and line parameters
Figure BDA0002476956600000081
In table PrefThe value of the rated power of the converter station 2 is negative for the reference power of each converter station, which indicates that the converter station injects active power from the dc system to the ac system.
The node voltage and the load flow distribution condition of the direct current power grid can be obtained by carrying out load flow calculation on the direct current power grid, and are shown in a table 2:
table 2 dc network load flow calculation results
Figure BDA0002476956600000082
Table 3 shows the screening results for the DC CFC target line, which shows that the exception of L12Besides, other lines all meet the installation requirement of the DC CFC, and the DC CFC can be installed. I.e. the target line set gamma contains the division L12The outer 5 elements.
TABLE 3 screening results of DC CFC target line
Figure BDA0002476956600000083
And then, main DC CFC addressing is carried out under the normal operation condition. Table 4 shows the results of the comprehensive safety index calculation and the main DC CFC site selection of the improved Zhoushan direct current transmission system, and CI in the set gamma is selectedpqHighest value line L14As a main control line for the main DC CFC, at L14In the line connected with two-end converter stationsSelecting CIpqLowest value line L45As an auxiliary control line for the main DC CFC.
TABLE 4 improved comprehensive safety index calculation and main DC CFC addressing for Zhoushan direct current transmission system
Figure BDA0002476956600000091
And then, carrying out standby DC CFC addressing under the N-1 operation condition.
And (4) carrying out N-1 fault analysis on all lines in the power grid. Table 5 shows the comprehensive performance index conditions and fault set classifications of the lines under different N-1 faults, and analysis shows that when N-1 faults occur in 6 lines, if and only if L faults occur14When the system is open-circuit, the system can not realize the safe and stable operation of the line by the cooperation of the converter station and the main DC CFC, namely, a fault set delta2Non-empty and therefore require the installation of a DC CFC.
TABLE 5 line comprehensive performance index conditions and fault classifications under different N-1 fault conditions
Figure BDA0002476956600000092
Calculating delta2In, L14System safety index CI under faultsumAnd calculating the CI of the line in the set gamma under the fault conditionpqWeighted averages, arranged in descending order, give table 6. Selecting CIpqLine L with highest weighted average15As a standby DC CFC, in a determined main control line L15Selecting the circuit connected with the two-end converter stations to be located in the set gamma and CIpqLine L with lowest weighted average13As a DC CFC auxiliary control circuit.
TABLE 4L14Improved Zhoushan direct current transmission system comprehensive safety index calculation and standby DC CFC site selection under fault
Figure BDA0002476956600000101
So far, the DC CFC site selection is completed, and a five-terminal direct current power grid topological diagram after two additional DC CFCs are added is shown in the attached figure 4.
And then performing DC CFC capacity multi-target optimization. The two selected places in the previous section are provided with DC CFCs, and a genetic algorithm is adopted to carry out DCCFC capacity optimization aiming at safety and economy on a direct current power grid containing the DC CFCs, wherein the same weight coefficient, namely omega, is assigned to the optimization indexes of the safety and the economy of the power grid operation in the multi-objective optimization process1＝ω2＝ω3. The multi-objective optimization function iteration curve is shown in figure 5. It can be seen from fig. 5 that the objective function value is obviously reduced after optimization, and the values of the variables after optimization are shown in table 5.
TABLE 5 optimized values of variables
Figure BDA0002476956600000102
In the table: smain-series1For main DC CFC main control line converter capacity, Smain-series2For main DC CFC auxiliary control line converter capacity, Sspare-series1For standby DC CFC main control line converter capacity, Sspare-series2Auxiliary control of line converter capacity for standby DC CFC, I14refAnd I15refThe main control line current instruction values controlled by the main DC CFC and the standby DC CFC. The results of the table 5 are combined, the UPFC engineering at home and abroad is used for reference, the redundancy of 5% -10% is set, the capacity of the main DC CFC converter is set to be 2 x 70MW, the capacity of the standby DC CFC converter is set to be 2 x 80MW, the engineering application requirements can be met, and meanwhile, the capacity cost and the tidal current regulation capacity of the DC CFC can be considered. Table 6 shows the values of the main state variables of the system before and after optimization, and it can be seen that on the premise of satisfying the minimum steady-state operation capacity of the DC CFC, the line power flow is more balanced after optimization, and the DC output voltage offset rate of the converter station is lower, which increases the power flow transmission capability and the power transmission safety of the DC power grid.
TABLE 6 variable values of main state variables of system before and after optimization
Figure BDA0002476956600000103

Claims (7)

1. The method for the stepwise site selection and the multi-objective optimization constant volume of the current and power flow controller is characterized by comprising the following steps of:
step 1, inputting initial data of a power grid;
step 2, performing initial load flow calculation on the direct current network;
step 3, establishing a comprehensive index system for the direct-current power grid, wherein the comprehensive index system is used for considering the direct-current line load flow performance and the direct-current output voltage performance of the converter station;
step 4, screening all lines according to the DC CFC site selection principle to obtain a target line set gamma meeting the installation requirement;
step 5, selecting the main DC CFC site under the normal operation condition;
6, selecting the standby DC CFC address under the operation condition of N-1;
step 7, taking economic and safety indexes as comprehensive evaluation indexes, establishing a DC CFC capacity multi-target optimization function, and converting multi-target optimization into single-target optimization by adopting a linear combination optimization method with conversion weighting;
step 8, establishing an optimized constraint condition by using the constraint of a conventional power system and the constraint of the internal power of the DC CFC;
and 9, taking the capacity of the DC CFC main control circuit/auxiliary control circuit converter as a variable to be optimized, optimizing by using a genetic algorithm to obtain the optimal capacity, and completing volume fixing.
2. The coupling sensitivity analysis-based current power flow controller addressing method according to claim 1, wherein in step 3, a comprehensive index system considering dc line power flow performance and converter station dc output voltage performance is established for the dc power grid, specifically:
1) DC line tidal current performance index
When the N-1 safety check is carried out on a direct current network, the distribution of an original system is greatly influenced, the power transmitted on each line is greatly changed, and a heavy load or even an overload line occurs, so that the safe operation of the system is influenced, and the direct current line tide performance index and the system tide performance index are provided to quantitatively describe the power flow performance of the power grid:
Figure FDA0002476956590000011
Figure FDA0002476956590000012
in formulae (1) to (2): i isP-pqIs a branch pq power flow performance index, IPIs a system tidal current performance index; ppqIs the active power flow on branch pq;
Figure FDA0002476956590000013
is the rated active power flow of the branch pq; n is an exponential coefficient and its value is a positive integer, usually taken as 1; alpha is a line set; omegapqIs a weight factor reflecting the importance of the branch;
thus defined IP-pqThe actual power flow is compared with the power flow limit intuitively, the margin between the actual power flow and the limit power flow can be reflected, the larger the numerical value of the margin, the closer the power flow on the line is to the system power flow limit value, the information of the blockage of the power transmission line is included, and when n is 1, IP-pqHas a normal value range of (0, 0.5)]Values higher than 0.5 mean that the line is in an overload state; through IP-pqAnd IPThe value of (1) can reflect the static safety state of the line pq and the line in the whole direct current power grid;
2) DC output voltage performance index of converter station
Defining a direct-current output voltage performance index of a direct-current power grid converter station, wherein the index is used for measuring the deviation degree of an outlet voltage operating point of the converter station and a reference operating point thereof:
Figure FDA0002476956590000021
Figure FDA0002476956590000022
Figure FDA0002476956590000023
Figure FDA0002476956590000024
in formulae (3) to (6): i isU-pIs a p DC output voltage performance index, I, of the converter stationUIs a system voltage performance indicator; u shapepIs the node p outlet voltage; m is an exponential coefficient and its value is a positive integer, usually taken as 1; beta is a converter station set; omegapIs a weight factor reflecting the importance of the converter station;
Figure FDA0002476956590000025
the upper and lower limits of the outlet voltage of the converter station p;
the voltage performance indexes of two ends of the line pq can be obtained by calculating the performance indexes of the outlet voltages of the p converter station and the q converter station:
Figure FDA0002476956590000026
in the formula (7), IU-pqThe offset of the voltage at two sides of the line pq is reflected, and is one of indexes for measuring the health condition of the line pq; i isUComprehensively reflecting the degree of deviation of the outlet voltage of each converter station of the direct-current power grid from a rated value, wherein the larger the value of the deviation is, the larger the outlet voltage deviation of the converter stations of the power grid is, and due to the existence of an index coefficient, the performance index is rapidly increased when the voltage is limited, and the voltage performance of the direct-current power grid is reflected to be poor; when m is 1, IU-pqHas a normal value range of [0,1 ]]A value higher than 1 means that the dc output voltage offset of at least 1 converter station on both sides of the line pq exceeds the limitA value;
3) comprehensive safety margin index
The health condition of the circuit pq can be obtained by comprehensively considering the active power flow performance of the circuit pq and the outlet voltage performance of the converter stations at two sides of the circuit pq, and the health condition is used as the comprehensive safety standard of CFC installation requirements:
Figure FDA0002476956590000031
using the above formula (8) as a comprehensive measure: CIpqAnd CIsumRespectively representing the comprehensive safety margin indexes of the line pq and the whole system; eta1、η2、μ1、μ2The parameter weights are respectively represented, and the importance degree of the parameters is reflected.
3. The current power flow controller addressing method based on coupling sensitivity analysis as claimed in claim 1, wherein in step 4, all lines are screened according to a DC CFC addressing principle to obtain a target line set γ meeting installation requirements, wherein the DC CFC addressing principle is as follows:
1) the DC CFC is required to be arranged in a direct current looped network;
2) when the line power flow can be completely controlled only by the converter station on the transmission line, the DC CFC does not need to be installed;
3) the converter station at the DC CFC installation node is provided with at least two outgoing lines, and the DC CFC controls the power flow of at least two branches at the same time;
4) the DC CFC auxiliary control line must have sufficient capacity margin.
4. The coupling sensitivity analysis-based current-power flow controller addressing method as claimed in claim 1, wherein in step 5, the addressing of the main DC CFC under normal operation conditions specifically comprises:
1) under the normal operation condition of the system, the comprehensive performance index CI of the circuit is utilizedpqSorting each line in the set gamma, selecting CIpqThe line with the highest value is used as a main control line of the main DC CFC;
2) in thatCI is selected from the determined lines connected with the converter stations at the two ends of the main control linepqThe lowest value line acts as the secondary control line for the main DC CFC.
5. The coupling sensitivity analysis-based current-power flow controller addressing method as claimed in claim 1, wherein in step 6, addressing of the standby DC CFC under N-1 operating conditions specifically comprises:
1) n-1 fault analysis is carried out on all lines in the power grid, and the performance index I of the lines can be ensured by controlling the converter station and the DC CFC after the faultsP-pqAnd IU-pqThe fault set that all meet the system operation requirements is recorded as fault set delta1And other faults are recorded as a fault set delta2. Determination of delta2If the current set is an empty set, if so, ending the step 6, otherwise, entering the next step;
2) finding delta2System safety index CI under fault of each linesumUsing CIsumFor fault set delta2The line faults in the system are sorted according to severity, and a plurality of more serious line fault conditions (such as simple power grid or delta) are selected2And (3) less internal elements, and all line fault conditions can be selected for calculation): calculating CI of lines in fault condition in set gamma according to importance degree of linespqA weighted average;
3) selecting CIpqThe line with the highest weighted average value is used as the main control line of the standby DC CFC, and the CI which is positioned in the set gamma is selected from the lines connected by the converter stations at the two ends of the determined main control linepqThe line with the lowest weighted average value is used as the DC CFC auxiliary control line;
4) judging whether the DC CFC still needs to be installed, if so, returning to the step 6-3) to select CIpqThe line with the next highest weighted average serves as the primary line for the standby DC CFC and completes the procedure, otherwise, the procedure is ended.
6. The current power flow controller site selection method based on coupling sensitivity analysis as claimed in claim 1, wherein in step 7, economic and safety indexes are taken as comprehensive evaluation indexes, a DC CFC capacity multi-objective optimization function is established, and a linear combination optimization method with conversion weighting is adopted to convert multi-objective optimization into single-objective optimization, specifically:
1) objective function
Figure FDA0002476956590000041
Figure FDA0002476956590000042
Figure FDA0002476956590000043
In the formula (9), IPIs a DC line power flow performance index; ppqIs the active power flow on branch pq;
Figure FDA0002476956590000044
is the nominal delivery capacity of the branch pq; n is an exponential coefficient and its value is a positive integer; alpha is a converter station set; omegapqIs a weight factor reflecting the importance of the branch; formula (10), wherein IUIs the performance index of the direct current output voltage of the converter station; u shapepIs the dc outlet voltage of the converter station pddc; m is an exponential coefficient and its value is a positive integer; beta is a converter station set; omegapIs a weight factor reflecting the importance of the converter station; in the formula (11), f (S) is a DC CFC construction cost function, wherein a, b and c are price constants, a is more than 1, b is more than 1, and c is more than 1; s1、S2For DC CFC main control (auxiliary control) line converter capacity, nyThe economic operating life of the DC CFC;
2) converting multi-objective optimization into single-objective optimization
The above-mentioned consideration of electric power system operation security and economic nature index forms the multi-objective optimization function:
Figure FDA0002476956590000045
for the multi-objective optimization function formula (12), the NSGA-2 algorithm can be adopted to find as many Pareto optimal solution sets as possible, but it is difficult to decide a satisfactory solution from the Pareto optimal solution sets. Thus, the conversion weighting method is adopted to optimize the function f by the partial target using the sine conversion function in FIG. 2p(X) conversion to a dimensionless and equal-magnitude objective function
Figure FDA0002476956590000051
Then using the converted partial objective function and the weighting factor omegapForming a new unified target function:
Figure FDA0002476956590000052
in formula (13), ωpOptimizing weight coefficients for multiple objectives, where ω1、ω2The method is the weight of the safety index, and reflects the attention degree, omega, of the requirement on the operation safety of the direct current power grid3The method occupies the weight for the economic indexes, and reflects the attention degree of the power grid operation economic requirement; note here that f in the sinusoidal transfer functionpUpper limit of (X) < beta >pThe value of (a) is not necessarily selected according to physical limits and can be further reduced according to optimization objectives.
7. The coupling sensitivity analysis-based current-power flow controller addressing method as claimed in claim 1, wherein in step 8, the optimization constraint conditions are established according to the conventional power system constraint and the DC CFC internal power constraint, wherein the constraint conditions introduced for the DC CFC are:
Figure FDA0002476956590000053
Figure FDA0002476956590000054
in the formula (14), Delta I is a current error term IijrefA current command value set for the line ij; in the formula (15), Δ PbbiAdditional injection power, δ P, introduced for DC CFC at node iijAdditional injection power, deltaP, introduced on line ij close to node i for the DC CFCikThe same process is carried out;
Figure FDA0002476956590000055
Figure FDA0002476956590000056
in formula (16), Udcp、PdcpRespectively injecting the active power of the direct current power grid into the voltage p and the change point of any node of the direct current power grid; in the formula (17), eij、eikThe equivalent direct current voltage is introduced into the DC CFC main control and auxiliary control circuit.
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