CN108988376B - Method, system and device for determining short-circuit current on alternating current side and readable storage medium - Google Patents

Method, system and device for determining short-circuit current on alternating current side and readable storage medium Download PDF

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CN108988376B
CN108988376B CN201810972595.5A CN201810972595A CN108988376B CN 108988376 B CN108988376 B CN 108988376B CN 201810972595 A CN201810972595 A CN 201810972595A CN 108988376 B CN108988376 B CN 108988376B
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hvdc
power grid
alternating current
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CN108988376A (en
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屠卿瑞
曾耿晖
李一泉
陈桥平
刘若平
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Guangdong Power Grid Co Ltd
Electric Power Dispatch Control Center of Guangdong Power Grid Co Ltd
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Huazhong University of Science and Technology
Guangdong Power Grid Co Ltd
Electric Power Dispatch Control Center of Guangdong Power Grid Co Ltd
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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
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/06—Measuring real component; Measuring reactive component
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • 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]

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Abstract

The application discloses a method, a system and a device for determining short-circuit current on an MMC-HVDC alternating current side and a readable storage medium, wherein the method comprises the following steps: obtaining active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails; calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current; and establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current, and calculating the short-circuit current on the alternating current side according to the equivalent circuit model. According to the invention, the three-phase current output by the converter side is obtained through the active current and the reactive current, the three-phase current is brought into the equivalent circuit model, the MMC-HVDC response characteristic in the fault of the alternating current side is researched, the MMC-HVDC equivalent model suitable for the alternating current protection setting calculation is established, and the accuracy of the calculation of the short-circuit current at the alternating current side of the MMC-HVDC system is improved.

Description

Method, system and device for determining short-circuit current on alternating current side and readable storage medium
Technical Field
The invention relates to the technical field of alternating current protection, in particular to a method, a system and a device for determining a short-circuit current on an alternating current side of MMC-HVDC and a readable storage medium.
Background
The AC protection setting calculation is an important basic work for guaranteeing the safe operation of a power grid, and the protection setting calculation is the most complex and most important component part with the largest workload in the setting calculation due to the existence of the coordination and coordination relationship among the protections. With the development of the alternating current power grid, related research is gradually perfected.
In recent years, with the change of energy situation and the progress of power grid technology, the development of flexible direct current (VSC-HVDC) technology is promoted, and modular multilevel high voltage direct current (MMC-HVDC) based high voltage direct current (transmission based on modular multilevel converter) has attracted wide attention worldwide by virtue of its unique advantages, and fig. 1 is an MMC-HVDC system single-ended equivalent topological diagram. With the large scale access of MMC-HVDC in the grid, dc power electronics have a new impact on the system fault characteristics.
When a direct current side fault or a converter internal fault occurs in the MMC-HVDC, the converter is usually locked quickly based on a flexible direct current system self-protection strategy, so that no short-circuit current is injected into a fault point, and therefore the alternating current system is less influenced; when an alternating current side fault occurs, the MMC-HVDC has low voltage ride through capability, and the MMC-HVDC is continuously hung on a power grid to operate, so that the fault current is influenced. Especially in connection with weak ac systems, the short-circuit current provided by MMC-HVDC is not negligible compared to the short-circuit current provided by the ac system itself.
At present, the response of a direct current system and direct current control is not considered in the alternating current protection setting calculation, and the contribution of MMC-HVDC to short-circuit current when the alternating current system fails is ignored. Therefore, the problems that the MMC-HVDC has influence on the short-circuit current when the alternating current side fails, how the MMC-HVDC should handle when the alternating current protection setting calculation is carried out and the like need to be researched. The existing research about the MMC-HVDC alternating-current side short-circuit current determination method is mainly aimed at alternating-current side symmetrical short circuit, and for alternating-current side asymmetrical faults, the existing research is mainly focused on analysis of bridge arm ring current and submodule capacitor voltage under an unbalanced operation state of an alternating-current side, influence on a control system and improvement on the control system. From the perspective of alternating current protection, calculation of short-circuit current on the alternating current side of the MMC-HVDC is not researched, so that the correctness and the rationality of the setting value of the alternating current protection are restricted.
Therefore, how to provide a solution to the above technical problems is a problem to be solved by those skilled in the art.
Disclosure of Invention
In view of the above, an objective of the present invention is to provide a method, a system, a device, and a readable storage medium for determining an MMC-HVDC ac short-circuit current, so as to incorporate the MMC-HVDC ac short-circuit current into a fault short-circuit analysis of an ac power grid, and obtain more accurate short-circuit data. The specific scheme is as follows:
a method for determining short-circuit current on an alternating current side of MMC-HVDC comprises the following steps:
obtaining active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails;
calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current;
and establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current, and calculating the short-circuit current at the alternating current side according to the equivalent circuit model.
Preferably, before determining the active current and the reactive current output by the target MMC-HVDC system in the event of the ac grid fault, the method further includes:
evaluating all MMC-HVDC systems accessed to the alternating current power grid to obtain the power grid contribution of each MMC-HVDC system;
and judging the MMC-HVDC system with the power grid contribution exceeding a preset value as the target MMC-HVDC system.
Preferably, the power grid contribution amount is specifically:
and when each MMC-HVDC system is connected to the alternating current power grid, the voltage change amount of the fault point is changed.
Preferably, the process of evaluating all MMC-HVDC systems accessing the ac power grid to obtain the power grid contribution of each MMC-HVDC system specifically includes:
respectively acquiring the maximum injectable current of each MMC-HVDC system to the alternating current power grid;
obtaining the mutual impedance between each MMC-HVDC system and the fault point;
evaluating each of the MMC-HVDC systems according to the maximum injectable current and the mutual impedance to obtain a corresponding grid contribution.
Preferably, the process of respectively obtaining the maximum injectable current of each MMC-HVDC system to the ac power grid specifically includes:
according to the formula
Figure BDA0001776586260000031
Calculating the maximum injectable current of each MMC-HVDC system to the alternating current power grid; wherein, IfFor the maximum injectable current, id maxAnd iq maxAnd sequentially setting an active current reference value and a reactive current reference value of each MMC-HVDC system.
Preferably, the process of evaluating each of the MMC-HVDC systems according to the maximum injectable current and the transimpedance to obtain the corresponding grid contribution specifically includes:
according to the formula
Figure BDA0001776586260000032
Calculating the contribution of the power grid, wherein a node j is any one of the MMC-HVDC systems in all the MMC-HVDC systems H, a node f is the fault point, and Z isfjIs the mutual impedance between nodes j, f, IjThe maximum injectable current at node j.
Preferably, the process of calculating a three-phase current output by a converter side of the target MMC-HVDC system according to the active current and the reactive current specifically includes:
calculating the three-phase current by the following relation:
Figure BDA0001776586260000033
wherein idAnd iqIn turn being the active current and the reactive current ima、imbAnd imcThe three-phase current is sequentially generated.
Correspondingly, the invention also discloses a system for determining the short-circuit current at the AC side of the MMC-HVDC, which comprises the following steps:
the acquisition module is used for acquiring active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails;
the calculation module is used for calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current;
and the equivalent module is used for establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current and calculating the short-circuit current at the alternating current side according to the equivalent circuit model.
Correspondingly, the invention also discloses a device for determining the short-circuit current on the AC side of the MMC-HVDC, which comprises the following components:
a memory for storing a computer program;
a processor for implementing the steps of the method for determining a short-circuit current on the ac-side of MMC-HVDC as described above when executing said computer program.
Correspondingly, the invention also discloses a readable storage medium, which is characterized in that the readable storage medium stores thereon a computer program, which when executed by a processor implements the steps of the method for determining a short-circuit current on the ac side of MMC-HVDC as described above.
The invention discloses a method for determining short-circuit current on an MMC-HVDC alternating current side, which comprises the following steps: obtaining active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails; calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current; and establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current, and calculating the short-circuit current at the alternating current side according to the equivalent circuit model. According to the invention, the three-phase current output by the converter side is obtained through the determined active current and reactive current, then the three-phase current is brought into the equivalent circuit model, the MMC-HVDC response characteristic in the case of an alternating current side fault is researched, the MMC-HVDC equivalent model suitable for alternating current protection setting calculation is established, and the accuracy of calculation of the short-circuit current at the alternating current side of the MMC-HVDC system is improved.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a single-ended equivalent topology diagram of a MMC-HVDC system in the prior art;
FIG. 2 is a flowchart illustrating steps of a method for determining a short-circuit current on an AC side of MMC-HVDC according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an equivalent circuit of a single direction when the AC side of the MMC-HVDC is short-circuited in the embodiment of the present invention;
FIG. 4 is an equivalent circuit model of an AC power grid and a target MMC-HVDC in an embodiment of the present invention;
fig. 5 is a flow chart of a sub-step of a method for determining a short-circuit current on an ac side of an MMC-HVDC converter in an embodiment of the present invention;
FIG. 6a is a diagram illustrating DC-side response characteristics of an MMC-HVDC according to an embodiment of the present invention;
FIG. 6b is a diagram illustrating DC-side response characteristics of an MMC-HVDC according to an embodiment of the present invention;
FIG. 6c is a diagram illustrating DC-side response characteristics of an MMC-HVDC according to an embodiment of the present invention;
fig. 7 is a structural distribution diagram of a system for determining an ac-side short-circuit current in an MMC-HVDC converter according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention discloses a method for determining short-circuit current on an MMC-HVDC alternating-current side, which is shown in figure 2 and comprises the following steps:
s1: determining an active current i output by a target MMC-HVDC system upon failure at a point of failure of an AC power griddAnd a reactive current iq；
Wherein the trend of active current and reactive current after the fault occurs at the fault point is gradually increased.
In particular, the reference value of the active current
Figure BDA0001776586260000051
Is composed of
Figure BDA0001776586260000052
Wherein A isrefRepresenting the set value of active power or direct voltage, A representing the actual value of active power or direct voltage, KdPIs a proportionality coefficient, KdIIs an integral coefficient. When the active power output by the converter is reduced or the direct current voltage is reduced after the fault, and the set value of the active power or the direct current voltage is not changed, ArefA increases, so after failure
Figure BDA0001776586260000053
Increase, finally increase to idmax。
Similarly, reference value of reactive current
Figure BDA0001776586260000054
Is composed of
Figure BDA0001776586260000055
Wherein B isrefRepresenting a set value of reactive power or alternating voltage, B representing an actual value of reactive power or alternating voltage, KqPIs a proportionality coefficient, KqIIs an integral coefficient. The reactive power output by the inverter after a fault decreases (ac voltage drop) without changing the set value, BrefB increases, so after failure
Figure BDA0001776586260000056
Increase, finally increase to iqmax。
S2: according to the active current idAnd the reactive current iqCalculating the three-phase current i output by the current converter side of the target MMC-HVDC systemma、imbAnd imc；
The method for calculating the three-phase current output by the current transformer comprises the following steps:
Figure BDA0001776586260000061
because the control system enables the converter to still output symmetrical current under the condition of asymmetrical fault of the alternating current side, zero-axis component i00, therefore, the above formula is converted to the following formula in the present embodiment:
Figure BDA0001776586260000062
wherein
Figure BDA0001776586260000063
S3: and establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current, and calculating the short-circuit current at the alternating current side according to the equivalent circuit model.
It can be seen that, since the active current and the reactive current are converted into three-phase currents in step S2, the target MMC-HVDC system is equivalent to a positive sequence current source in step S3, and an equivalent circuit model is established together with the ac power grid.
More specifically, in order to avoid the problems of overlarge setting calculation amount, overlow calculation efficiency, limited power grid modeling scale and the like caused by accurate modeling, the equivalent circuit model is simplified to a certain extent, firstly, the change of a fault process along with time is not considered, and the attenuation of short-circuit current is not considered; the other is to use static elements to simulate dynamic elements.
According to the equivalent circuit model, the sequence network equation when a fault point fails can be written as follows:
Figure BDA0001776586260000064
Figure BDA0001776586260000065
Figure BDA0001776586260000066
in the formula
Figure BDA0001776586260000067
And
Figure BDA0001776586260000068
three-sequence voltage, X, of phase a at the fault pointff(1)、Xff(2)、Xff(0)Three-sequence reactances of relative fault points in the equivalent circuit model respectively,
Figure BDA0001776586260000069
the three-sequence current of the phase a of the fault point respectively, the set H comprises all MMC-HVDC systems connected with the alternating current power grid, the set G comprises other power transmission systems which are not MMC-HVDC systems in all power transmission systems connected with the alternating current power grid, and ZfjAnd
Figure BDA00017765862600000610
respectively the impedance and current of a certain transmission system j with respect to the point of failure.
Similarly, at this time, the three-sequence voltages at any node i in the equivalent circuit model are respectively:
Figure BDA0001776586260000071
Figure BDA0001776586260000072
Figure BDA0001776586260000073
in the formula Zif(1)、Zif(2)And Zif(0)Respectively, the three-sequence impedance of the node Ij∠-θjIs the current phasor for any power transmission system j.
Further, according to the above two equations, it can be determined that the phase a current flowing through any branch ij is:
Figure BDA0001776586260000074
Figure BDA0001776586260000075
Figure BDA0001776586260000076
in the formula
Figure BDA0001776586260000077
And
Figure BDA0001776586260000078
the a-phase three-sequence current of the branch ij,
Figure BDA0001776586260000079
and
Figure BDA00017765862600000710
respectively the three-sequence voltage of the power transmission system i,
Figure BDA00017765862600000711
and
Figure BDA00017765862600000712
three-sequence voltage, x, of the transmission system j, respectivelyij(1)、xij(2)And xij(0)Respectively, the triple-order reactance between the two points ij.
Reference can be made to the one-way equivalent circuit diagram of the MMC-HVDC ac side short circuit in fig. 3, and the equivalent circuit model of the ac grid and the target MMC-HVDC in fig. 4.
According to the content, the calculation of the short-circuit current at the alternating current side and the setting calculation in a subsequent alternating current grid system can be carried out on the determination of the short-circuit current at the alternating current side of the MMC-HVDC and the established equivalent circuit model.
The embodiment of the invention discloses a method for determining short-circuit current on an MMC-HVDC alternating-current side, which comprises the following steps: obtaining active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails; calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current; and establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current, and calculating the short-circuit current at the alternating current side according to the equivalent circuit model. According to the invention, the three-phase current output by the converter side is obtained through the determined active current and reactive current, then the three-phase current is brought into the equivalent circuit model, the MMC-HVDC response characteristic in the case of an alternating current side fault is researched, the MMC-HVDC equivalent model suitable for alternating current protection setting calculation is established, and the accuracy of calculation of the short-circuit current at the alternating current side of the MMC-HVDC system is improved.
The embodiment of the invention discloses a specific MMC-HVDC alternating-current side short-circuit current determination method, and compared with the previous embodiment, the embodiment further explains and optimizes the technical scheme. See specifically fig. 5:
before determining the active current and the reactive current output by the target MMC-HVDC system in the event of the ac grid fault at step S1, the method further includes:
s01: evaluating all MMC-HVDC systems accessed to the alternating current power grid to obtain the power grid contribution of each MMC-HVDC system;
s02: and judging the MMC-HVDC system with the power grid contribution exceeding a preset value as the target MMC-HVDC system.
It will be appreciated that not all MMC-HVDC systems need to take fault considerations into account, and that some MMC-HVDC systems do not contribute significantly to a fault in the ac grid itself, which is why the short circuit provided by MMC-HVDC is ignored in the prior art. Therefore, in the embodiment, all the MMC-HVDC systems are evaluated, and the MMC-HVDC system with the power grid contribution exceeding the preset value is set as the target MMC-HVDC system.
The power grid contribution amount is specifically as follows: and when each MMC-HVDC system is connected to the alternating current power grid, the voltage change amount of the fault point is changed.
More specifically, the step S01 is a process of evaluating all MMC-HVDC systems accessing the ac power grid to obtain a power grid contribution of each MMC-HVDC system, and specifically includes:
s011: respectively acquiring the maximum injectable current of each MMC-HVDC system to the alternating current power grid;
in particular, according to the formula
Figure BDA0001776586260000081
Calculating the maximum injectable current of each MMC-HVDC system to the alternating current power grid; wherein, IfFor the maximum injectable current, id maxAnd iq maxAnd sequentially setting an active current reference value and a reactive current reference value of each MMC-HVDC system.
It can be seen that the maximum injectable current is actually determined by the control system, the inner loop current controller limiting the bridge arm by limiting the active and reactive current reference valuesI.e. the maximum injectable current. Active current i after the fault occurs in the previous embodimentdAnd a reactive current iqFinally increase to id maxAnd iq maxIt is controlled by the inner loop current controller in this embodiment.
See the MMC-HVDC direct current side response characteristic diagrams of fig. 6a, 6b, 6 c. In each figure, the radius of the outer circle is 1, the radius of the inner circle is 0.5, and U isSIs an alternating system voltage; FIG. 6a represents the corresponding current phasor at the DC side, I, in the rectification modemRRepresenting the direct current side response current vector in the rectification mode, i before the fault of the rectification moded＝1,iq0; FIG. 6b represents the DC-side corresponding current phasor in the inverter mode, ImI represents the DC-side response current phasor in the inverter mode, i before the inverter mode failured＝-1,iq0; FIG. 6c represents the corresponding current phasor at the DC side, I, for the STATCOM modemSRepresenting direct current side response current vector in STATCOM mode, i before STATCOM mode failured＝0,iq-0.45; in the event of a fault, | id max|＝0.85,|iq maxAnd | ═ 0.45. Specifically, 4 vectors in each figure are direct-current side response current vectors when 4 types of faults of single-phase ground short circuit, two-phase interphase short circuit and three-phase short circuit occur respectively. In addition thereto, id、iqIs artificially set according to the system operation requirements, e.g. how much transmission power isd max，iq maxIs based on power electronics) current limit requirements.
S012: obtaining the mutual impedance between each MMC-HVDC system and the fault point;
the mutual impedance can be obtained by setting an asymmetric fault at a fault point and calculating the ratio of negative sequence voltage output by an MMC-HVDC system access bus and negative sequence current at the fault point.
S013: evaluating each of the MMC-HVDC systems according to the maximum injectable current and the mutual impedance to obtain a corresponding grid contribution.
According to the formula
Figure BDA0001776586260000091
Calculating the contribution of the power grid, wherein a node j is any one of the MMC-HVDC systems in all the MMC-HVDC systems H, a node f is the fault point, and Z isfjIs the mutual impedance between nodes j, f, IjThe maximum injectable current at node j.
In a particular embodiment, the grid contribution is consistent with the short circuit ratio. When only one MMC-HVDC system is accessed and the fault port and the flexible direct access position are consistent, the calculation formula of the power grid contribution amount can be rewritten into
Figure BDA0001776586260000092
Then derived to obtain
Figure BDA0001776586260000093
The power grid contribution delta and the short-circuit ratio index K can be seenSCRThe consistency is provided, and all the consistency is related to parameters such as equivalent impedance of an alternating current system at a fault point access position, system transmission power and the like. When the alternating current system is weaker, the equivalent impedance is larger, and the system transmission power is larger, the influence of the access of the MMC-HVDC system on the alternating current power grid is larger.
Further, the preset value of the grid contribution amount in step S02 may be set to 10%, and once the grid contribution amount exceeds 10%, the MMC-HVDC is determined as the target MMC-HVDC, and the influence of the MMC-HVDC is considered when an equivalent circuit model is established and a setting calculation is performed later.
Correspondingly, the embodiment of the invention also discloses a system for determining the short-circuit current on the ac side of the MMC-HVDC converter, as shown in fig. 7, including:
the system comprises an acquisition module 1, a fault detection module and a fault detection module, wherein the acquisition module 1 is used for acquiring active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails;
the calculation module 2 is used for calculating a three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current;
and the equivalent module 3 is used for establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current and calculating the short-circuit current at the alternating current side according to the equivalent circuit model.
The present embodiment has the same beneficial effects as the determination method of the short-circuit current on the ac side of the MMC-HVDC converter in the above embodiments, and details are not repeated here.
Correspondingly, the embodiment of the invention also discloses a device for determining the short-circuit current on the AC side of the MMC-HVDC, which comprises the following steps:
a memory for storing a computer program;
a processor for implementing the steps of the method for determining a short-circuit current on the ac-side of MMC-HVDC as described in the above embodiments when executing said computer program.
Specifically, for the detailed description of the method for determining the short-circuit current on the ac side of the MMC-HVDC converter, reference may be made to the above embodiments, which are not repeated herein.
The present embodiment has the same beneficial effects as the determination method of the short-circuit current on the ac side of the MMC-HVDC converter in the above embodiments, and details are not repeated here.
Correspondingly, the embodiment of the invention also discloses a readable storage medium, which is characterized in that the readable storage medium stores thereon a computer program, and the computer program, when executed by a processor, implements the steps of the method for determining the short-circuit current on the ac side of the MMC-HVDC converter as described above.
Specifically, for the detailed description of the method for determining the short-circuit current on the ac side of the MMC-HVDC converter, reference may be made to the above embodiments, which are not repeated herein.
The present embodiment has the same beneficial effects as the determination method of the short-circuit current on the ac side of the MMC-HVDC converter in the above embodiments, and details are not repeated here.
Finally, it should also be noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The method, the system, the device and the readable storage medium for determining the short-circuit current on the ac side of the MMC-HVDC converter provided by the present invention are described in detail, and a specific example is applied in the description to explain the principle and the implementation of the present invention, and the description of the above example is only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

Claims (8)

1. A method for determining short-circuit current on an alternating current side of MMC-HVDC is characterized by comprising the following steps:
obtaining active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails;
calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current;
establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current, and calculating the short-circuit current at the alternating current side according to the equivalent circuit model;
before determining the active current and the reactive current output by the target MMC-HVDC system when the alternating current power grid fails, the method further comprises the following steps:
evaluating all MMC-HVDC systems accessed to the alternating current power grid to obtain the power grid contribution of each MMC-HVDC system;
judging the MMC-HVDC system with the power grid contribution exceeding a preset value as the target MMC-HVDC system;
the power grid contribution amount is specifically as follows:
and when each MMC-HVDC system is connected to the alternating current power grid, the voltage change amount of the fault point is changed.
2. The method according to claim 1, wherein the step of evaluating all MMC-HVDC systems accessing the ac grid to obtain the grid contribution of each of the MMC-HVDC systems comprises:
respectively acquiring the maximum injectable current of each MMC-HVDC system to the alternating current power grid;
obtaining the mutual impedance between each MMC-HVDC system and the fault point;
evaluating each of the MMC-HVDC systems according to the maximum injectable current and the mutual impedance to obtain a corresponding grid contribution.
3. The method according to claim 2, wherein the step of obtaining the maximum injectable current of each MMC-HVDC system to the ac power grid comprises:
according to the formula
Figure FDA0003247969490000011
Calculating the maximum injectable current of each MMC-HVDC system to the alternating current power grid; wherein, IfFor the maximum injectable current, idmaxAnd iqmaxAnd sequentially setting an active current reference value and a reactive current reference value of each MMC-HVDC system.
4. The method for determining according to claim 3, wherein said process of evaluating each of said MMC-HVDC systems according to said maximum injectable current and said mutual impedance to obtain a corresponding grid contribution, comprises:
according to the formula
Figure FDA0003247969490000021
Calculating the contribution of the power grid, wherein a node j is any one of the MMC-HVDC systems in all the MMC-HVDC systems H, a node f is the fault point, and Z isfjIs the mutual impedance between nodes j, f, IjThe maximum injectable current at node j.
5. The method for determining according to any one of claims 1 to 4, wherein the step of calculating the three-phase current output by the converter side of the target MMC-HVDC system according to the active current and the reactive current comprises:
calculating the three-phase current by the following relation:
Figure FDA0003247969490000022
wherein idAnd iqIn turn being the active current and the reactive current ima、imbAnd imcThe three-phase current is sequentially generated.
6. A system for determining a short-circuit current on an ac-side of an MMC-HVDC converter, comprising:
the acquisition module is used for acquiring active current and reactive current output by a target MMC-HVDC system when a fault point of an alternating current power grid fails;
the calculation module is used for calculating three-phase current output by a current converter side of the target MMC-HVDC system according to the active current and the reactive current;
the equivalent module is used for establishing an equivalent circuit model of the alternating current power grid and the target MMC-HVDC system according to the three-phase current and calculating the short-circuit current at the alternating current side according to the equivalent circuit model;
the obtaining module is further used for evaluating all MMC-HVDC systems connected to the alternating current power grid before determining active current and reactive current output by a target MMC-HVDC system when the alternating current power grid fails so as to obtain power grid contribution of each MMC-HVDC system, and judging that the MMC-HVDC system with the power grid contribution exceeding a preset value is the target MMC-HVDC system;
the power grid contribution amount is specifically the voltage change amount of the fault point when each MMC-HVDC system is connected to the alternating current power grid.
7. An apparatus for determining short-circuit current on AC side of MMC-HVDC, comprising:
a memory for storing a computer program;
a processor for implementing the steps of the method for determining an ac-side short-circuit current according to any one of claims 1 to 5 when executing said computer program.
8. Readable storage medium, characterized in that it has stored thereon a computer program which, when being executed by a processor, carries out the steps of the method for determining a short-circuit current on the ac-side of MMC-HVDC as defined in anyone of claims 1 to 5.
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