CN111769527B - Single-phase alternating current line protection method and system of alternating current and direct current system - Google Patents

Single-phase alternating current line protection method and system of alternating current and direct current system Download PDF

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CN111769527B
CN111769527B CN202010680712.8A CN202010680712A CN111769527B CN 111769527 B CN111769527 B CN 111769527B CN 202010680712 A CN202010680712 A CN 202010680712A CN 111769527 B CN111769527 B CN 111769527B
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phase
fault
bus
voltage
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CN111769527A (en
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马静
刘晨
周晓东
周易
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North China Electric Power University
Economic and Technological Research Institute of State Grid Shanxi Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
    • H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
    • 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
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • 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
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • 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
    • 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 invention relates to a single-phase alternating current line protection method and system of an alternating current and direct current system, belongs to the technical field of relay protection, and solves the problem that the existing protection method has low judgment accuracy due to misoperation or failure in protection of the alternating current and direct current system with rich harmonic waves and non-periodic components. The method comprises the following steps: collecting three-phase voltage and three-phase current of an inverter side alternating current bus and three-phase current of an inverter flowing to the alternating current bus; based on the AC-DC interconnected power grid zero-mode equivalent circuit, adopting a KCL theorem and a KVL theorem to obtain a voltage-current equation of a certain fault on an inverter side relative to an AC bus; obtaining a fault distance based on three-phase voltage and three-phase current of the alternating-current bus, three-phase current of the inverter flowing to the alternating-current bus and a voltage-current equation; and the fault type is judged, and the inverter side circuit breaker is controlled to execute corresponding action according to the generated circuit breaker control signal, so that the single-phase alternating current circuit is protected, and the applicability and the accuracy are improved.

Description

Single-phase alternating current line protection method and system of alternating current and direct current system
Technical Field
The invention relates to the technical field of relay protection, in particular to a single-phase alternating current line protection method and system of an alternating current-direct current system.
Background
When an alternating current line on an inversion side has a fault, an inversion station is easily influenced and fails in phase commutation, and the direct current system has strong nonlinear characteristics due to the flexible and quick control effect of the direct current system. In addition, when a commutation failure occurs, it is equivalent to that a fault is superimposed in the ac/dc system, and the dc system as an additional fault source brings a great challenge to the reliability of the ac protection operation.
When the phase-change failure occurs on the inversion side caused by the fault of the alternating current line, the direct current side can be equivalent to a controlled current source, the inverter injects a large amount of higher harmonics and non-periodic components into the alternating current system, and the non-periodic components have exponential attenuation characteristics and larger time constants. The fault characteristics of a direct current system can affect alternating current protection, and a Fourier algorithm can filter some higher harmonics, but the higher harmonics are affected by non-periodic components, so that a larger error is generated, and the accuracy of protection action is affected. And because the control reaction of the direct current system is very fast, the injected current of the direct current system is in a nonlinear characteristic after a fault occurs, and the injected current of the direct current system is difficult to express quantitatively by an expression.
The traditional protection method is mostly power frequency protection, and as the duty ratio of an alternating current circuit in a system is gradually improved, the traditional protection method has the possibility of false operation or failure operation for the protection of an alternating current and direct current system with rich harmonic and non-periodic components, so that the problem of low judgment accuracy is caused.
Disclosure of Invention
In view of the foregoing analysis, embodiments of the present invention provide a method and a system for protecting a single-phase ac line of an ac/dc system, so as to solve the problem of low determination accuracy due to false operation or false operation of the existing protection method for protecting the ac/dc system with rich harmonic and non-periodic components.
In one aspect, an embodiment of the present invention provides a method for protecting a single-phase ac line of an ac/dc system, including the following steps:
three-phase voltage u of alternating current bus on inversion side is collectedma,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idcc；
Based on the AC-DC interconnected power grid zero-mode equivalent circuit, adopting a KCL theorem and a KVL theorem to obtain a voltage-current equation of a certain fault on an inverter side relative to an AC bus;
three-phase voltage u based on alternating current busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation to obtain a fault distance;
judging the fault type based on the fault distance;
and generating a breaker control signal according to the fault type, and controlling the inverter side breaker to execute corresponding actions to realize the protection of the single-phase alternating-current line.
Further, the voltage-current equation of a certain fault on the inversion side related to the alternating current bus is as follows:
Figure BDA0002585716580000021
wherein the content of the first and second substances,
Figure BDA0002585716580000022
Figure BDA0002585716580000023
wherein z phase represents any fault phase of a, b and c phases, umzFor the z-phase voltage, i, of the AC busbar on the inverting sidemzFor the z-phase current, x, of the AC bus on the inverting sidejIs the coefficient of the voltage-current equation, j is 1,21、L11-mode resistance and inductance, k, of the AC line on the inverter sideRIs a zero-mode compensation coefficient, k, of the resistanceR＝(R0-R1)/3R1，R0Zero mode resistance, k, for the inverting side AC lineLIs a zero-mode compensation coefficient, k, of the inductanceL＝(L0-L1)/3L1，L0Zero-mode inductance, i, for the inverting side AC linem0For zero-mode current i at the inverter side AC busbar protectiondc0Is the zero mode current component of the inverting side.
Further, three-phase voltage u based on the alternating current busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd voltage-current equation to obtain fault distance, including：
Collecting three-phase voltage u of an inversion side alternating current bus in a time windowma,umb,umcThree-phase current i of AC busma,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccInputting the voltage current equation to obtain an overdetermined equation;
obtaining a coefficient of the over-determined equation based on a least square optimization function of Matlab, wherein the coefficient of the over-determined equation is the same as the coefficient of the voltage-current equation;
and obtaining the fault distance according to the coefficient of the over-determined equation.
Further, a calculation formula for obtaining the fault distance according to the coefficient of the over-determined equation is as follows:
ρ＝x1
where ρ is the failure distance.
Further, based on the fault distance, judging the fault type, sending a corresponding signal to the inverter side circuit breaker by the protection device according to the fault type, and executing corresponding actions by the circuit breaker based on the signal, wherein the actions comprise:
if the fault distance is less than the full length of the single-phase alternating-current line, the fault is an intra-area fault, the protection device sends a tripping signal to the inverter side breaker, and the breaker trips;
if the fault distance is larger than the total length of the single-phase alternating-current line, the fault is an out-of-area fault, and the protection device sends a locking signal to the inverter-side circuit breaker to lock the single-phase fault line.
In another aspect, an embodiment of the present invention provides a single-phase ac line protection system for an ac/dc system, including:
the data acquisition module is used for acquiring the three-phase voltage u of the AC bus on the inversion sidema,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idcc；
The protection calculation module is used for obtaining a voltage current equation of a certain fault on the inversion side related to the alternating current bus by adopting a KCL theorem and a KVL theorem according to the zero-mode equivalent circuit of the alternating current-direct current interconnected power grid;
a fault distance obtaining module for obtaining the three-phase voltage u of the AC busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation to obtain a fault distance;
and the protection action module is used for judging the fault type according to the fault distance, generating a circuit breaker control signal according to the fault type, and controlling the circuit breaker on the inversion side to execute corresponding actions so as to realize the protection of the single-phase alternating-current line.
Further, the voltage and current equation of a certain fault on the inversion side related to the alternating current bus obtained by the protection calculation module is as follows:
Figure BDA0002585716580000041
wherein the content of the first and second substances,
Figure BDA0002585716580000042
Figure BDA0002585716580000043
wherein z phase represents any fault phase of a, b and c phases, umzFor the z-phase voltage, i, of the AC busbar on the inverting sidemzFor the z-phase current, x, of the AC bus on the inverting sidejIs the coefficient of the voltage-current equation, j is 1,21、L11-mode resistance and inductance, k, of the AC line on the inverter sideRIs a zero-mode compensation coefficient, k, of the resistanceR＝(R0-R1)/3R1，R0Zero mode resistance, k, for the inverting side AC lineLIs a zero-mode compensation coefficient, k, of the inductanceL＝(L0-L1)/3L1，L0Zero-mode inductance, i, for the inverting side AC linem0For zero-mode current i at the inverter side AC busbar protectiondc0Is the zero mode current component of the inverting side.
Further, the fault distance obtaining module executes the following process:
collecting three-phase voltage u of an inversion side alternating current bus in a time windowma,umb,umcThree-phase current i of AC busma,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccInputting the voltage current equation to obtain an overdetermined equation;
obtaining a coefficient of the over-determined equation based on a least square optimization function of Matlab, wherein the coefficient of the over-determined equation is the same as the coefficient of the voltage-current equation;
and obtaining the fault distance according to the coefficient of the over-determined equation.
Further, a calculation formula for obtaining the fault distance according to the coefficient of the over-determined equation is as follows:
ρ＝x1
where ρ is the failure distance.
Further, the protection action module executes the following process:
if the fault distance is less than the full length of the single-phase alternating-current line, the fault is an intra-area fault, the protection device sends a tripping signal to the inverter side breaker, and the breaker trips;
if the fault distance is larger than the total length of the single-phase alternating-current line, the fault is an out-of-area fault, and the protection device sends a locking signal to the inverter-side circuit breaker to lock the single-phase fault line.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
1. a single-phase alternating current line protection method of an alternating current and direct current system provides support and basis for constructing a voltage and current equation of a certain fault related to an alternating current bus at the later stage by collecting three-phase voltage and current information of the alternating current bus at an inversion side, meanwhile, a voltage and current equation of the certain fault related to the alternating current bus is obtained by adopting KCL and KVL theorem, a fault distance is finally obtained, and then the type of the fault is judged according to the fault distance to realize the protection of the single-phase alternating current line.
2. The voltage-current equation of a certain fault on the inversion side related to the alternating current bus is obtained by the alternating current-direct current interconnected power grid zero-mode equivalent circuit and adopting the KCL theorem and the KVL theorem, so that a basic basis and support are provided for calculating the fault distance in the later period, and the method is simple, easy to implement and has important significance.
3. The method comprises the steps of obtaining an overdetermined equation with the equation number larger than a coefficient to be solved by bringing collected three-phase voltage of an alternating current bus, three-phase current of the alternating current bus and three-phase current of an inverter flowing to the alternating current bus into a voltage current equation, obtaining the coefficient of the overdetermined equation through a least square optimization function of Matlab, further obtaining a fault distance, and judging the type of the fault through the fault distance so as to enable a corresponding relay to act, realize protection on an alternating current circuit with a corresponding fault, realize simple calculation and improve the stability of an alternating current and direct current system.
4. The fault type is judged by comparing the fault distance with the full length of the single-phase alternating-current circuit, the protection device generates a circuit breaker control signal according to the fault type, and controls the circuit breaker on the inversion side to execute corresponding actions, so that the single-phase alternating-current circuit is protected, the judgment mode is simple and reliable, the accuracy is high, and the protection device is suitable for protecting an alternating-current and direct-current system rich in harmonic waves and non-periodic components.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a flow chart of a single phase AC line protection method for an AC/DC system;
FIG. 2 is a schematic diagram of an AC/DC power transmission system;
FIG. 3 is an equivalent circuit diagram of an inverter side AC/DC power transmission system;
FIG. 4 is a zero-mode equivalent circuit diagram of an AC/DC interconnected power grid;
FIG. 5 is a diagram of an AC/DC interconnection simulation model;
fig. 6 is a fault distance diagram obtained by setting a fault at a position 80km away from an inverter station on an ac line MN;
fig. 7 is a diagram of transition resistances obtained by setting a fault at a distance of 80km from the inverter station in the ac line MN;
fig. 8 is a diagram of a fault distance obtained by setting a fault at the end of an ac line MN;
fig. 9 is a diagram of transition resistance obtained by setting a fault at the end of an ac line MN;
fig. 10 is a structural view of a single-phase ac line protection system of the ac/dc system;
reference numerals:
100-a data acquisition module; 200-a protection calculation module; 300-fault distance obtaining module; 400-protection action module.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
The traditional protection method is mostly power frequency protection, and as the duty ratio of an alternating current circuit in a system is gradually improved, the traditional protection method has the possibility of false operation or failure operation for the protection of an alternating current and direct current system with rich harmonic and non-periodic components, so that the problem of lower accuracy of judging the fault distance is caused. The method comprises the steps of obtaining a voltage current equation of a certain fault on an inverter side relative to an alternating current bus through a KCL theorem and a KVL theorem, inputting three-phase voltage and three-phase current of the alternating current bus on the inverter side and three-phase current of an inverter flowing to the alternating current bus into the voltage current equation in a time window to obtain overdetermined equations with the equation quantity larger than a coefficient to be solved, obtaining the coefficient of the overdetermined equations based on a least square optimization function of Matlab to further obtain a fault distance, and finally judging the fault type according to the fault distance to ensure that a corresponding relay acts to realize the protection of the single-phase alternating current circuit, thereby solving the problem that the existing protection method has the possibility of false action or rejection to the protection of the alternating current and direct current systems with rich harmonic and non-periodic components and causes lower accuracy, the protection to the alternating current circuit of the alternating current and direct current system is realized, and the applicability and the stability of the alternating current and direct current system are improved.
A specific embodiment of the present invention discloses a method for protecting a single-phase ac line of an ac/dc system, as shown in fig. 1. The method comprises the following steps:
step S1, collecting three-phase voltage u of alternating current bus on inversion sidema,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idcc. Specifically, the three-phase voltage u of the inverter side AC bus is collectedma,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccThe method is the basis for constructing the over-determined equation through the voltage current equation at the later stage.
And S2, obtaining a voltage-current equation of a certain fault on the inversion side related to the alternating current bus by adopting a KCL theorem and a KVL theorem on the basis of the zero-mode equivalent circuit of the alternating current-direct current interconnected power grid.
Specifically, the zero-mode equivalent circuit of the AC-DC interconnected power grid is obtained according to the topological structure characteristics of the AC-DC interconnected system. As shown in the schematic diagram of a typical dc power transmission system in fig. 2, the rectifying side and the inverting side are both formed by connecting two 6-pulse inverters in series, and the transformers connected to the two inverters are connected in parallel to the ac bus of the inverting side. The two converter transformers respectively adopt Yd11 and Yy0 windings.
When the a-phase grounding fault occurs in the AC line, the equivalent circuit is shown in FIG. 3. Since the inverter-side transformer is grounded in a star shape on the ac side and in a delta or star shape on the inverter side via a resistor, the inverter is not included in the zero-mode path. When the ac line fails, the dc system does not inject a zero-mode component into the ac system. And decomposing the three-phase circuit time domain value into three module values (1 module, 2 modules and 0 module) by adopting Clark conversion. The transformation formula is as follows:
Figure BDA0002585716580000091
based on the conversion formula, the zero-mode equivalent circuit of the alternating current-direct current interconnected power grid when any phase of the alternating current line has a ground fault can be obtained.
For example, when a phase a has a ground fault, a zero-mode equivalent circuit of the ac-dc interconnected network is shown in fig. 4. Using the KCL theorem, AC line fault point current ifCan be expressed as:
if(t)＝ima(t)+ina(t)＝3(im0(t)+in0(t)) (2)
if(t)＝uf(t)/Rf (3)
wherein ima(t) phase A current, i, at the AC bus of line MN at time tna(t) the current flowing through the fault point to the N-side line at time t, im0For zero-mode current i at the inverter side AC busbar protectionn0Is a zero-mode current component of the N-side system, if(t) the current at the fault point at time t, ufFor the fault point voltage at time t, RfIs the transition resistance.
The expression of the zero-mode current after the fault point can be obtained by the two expressions:
Figure BDA0002585716580000092
the following equation can be written in accordance with the KVL theorem:
Figure BDA0002585716580000101
will be a formula
Figure BDA0002585716580000102
Substituting the above formula, the equation when the a phase fault of the inversion side can be:
Figure BDA0002585716580000103
voltage u at fault pointfCan be calculated from the voltage and current measured by the protection device, and u can be obtained from fig. 4fThe expression of (a) is:
Figure BDA0002585716580000104
wherein R is1,L11-mode resistance and inductance, k, of the line MNR＝(R0-R1)/3R1，kL＝(L0-L1)/3L1。
Will ufWhen the expression (7) is substituted into the expression (6), u can be eliminatedfObtaining a voltage-current equation of the inverter side a-phase fault related to the alternating current bus, wherein the method comprises the following simplification processes:
Figure BDA0002585716580000105
terms related to the alternating bus voltage and the alternating bus current in the formula are taken as variables, other terms are taken as coefficients,
instant game
Figure BDA0002585716580000111
The following voltage-current equation of the inverter side a-phase fault related to the alternating current bus can be obtained:
Figure BDA0002585716580000112
similarly, the voltage and current equations of the phases b and c related to the alternating current bus can be obtained through the zero-mode equivalent circuit of the alternating current-direct current interconnected power grid when the phases b and c are in fault, and the voltage and current equations of any one of the phases a, b and c related to the alternating current bus can be obtained through summarization, as shown in the following formula.
Preferably, the voltage-current equation of a certain fault on the inversion side related to the alternating current bus is as follows:
Figure BDA0002585716580000113
wherein the content of the first and second substances,
Figure BDA0002585716580000121
Figure BDA0002585716580000122
wherein z phase represents any fault phase of a, b and c phases, umzFor the z-phase voltage, i, of the AC busbar on the inverting sidemzFor the z-phase current, x, of the AC bus on the inverting sidejIs the coefficient of the voltage-current equation, j is 1,21、L11-mode resistance and inductance, k, of the AC line on the inverter sideRIs a zero-mode compensation coefficient, k, of the resistanceR＝(R0-R1)/3R1，R0Zero mode resistance, k, for the inverting side AC lineLIs a zero-mode compensation coefficient, k, of the inductanceL＝(L0-L1)/3L1，L0For inverting side ACZero mode inductance of the line, im0For zero-mode current i at the inverter side AC busbar protectiondc0Is the zero mode current component of the inverting side.
The voltage-current equation of a certain fault on the inversion side related to the alternating current bus is obtained by the alternating current-direct current interconnected power grid zero-mode equivalent circuit and adopting the KCL theorem and the KVL theorem, so that a basic basis and support are provided for calculating the fault distance in the later period, and the method is simple, easy to implement and has important significance.
Step S3, three-phase voltage u based on AC busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd obtaining a fault distance through a voltage current equation. Specifically, the collected three-phase voltage of the alternating-current bus, the collected three-phase current of the alternating-current bus and the collected three-phase current of the inverter flowing to the alternating-current bus are substituted into a voltage-current equation to obtain an overdetermined equation with the equation number larger than the coefficient to be solved, and the coefficient of the overdetermined equation is obtained through a least square optimization function of Matlab to further obtain the fault distance.
Preferably, the three-phase voltage u is based on an alternating current busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation, obtaining a fault distance, comprising:
s301, collecting three-phase voltage u of the inversion side alternating current bus in a period of time windowma,umb,umcThree-phase current i of AC busma,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccThe input voltage current equation obtains an overdetermined equation. Specifically, based on the voltage-current equation of the ac bus related to a certain fault obtained in step S2, 7 unknown coefficients need to be solved, and an overdetermined equation may be constructed by using the measurement data in a time window, where the collected measurement data is greater than 7 sets, and the collected data is largeAnd substituting the 7 groups of measurement data into a voltage-current equation to obtain an over-determined equation, wherein the number of the over-determined equations is greater than the number of the coefficients to be solved.
Step S302, obtaining a coefficient of an over-determined equation based on a least square optimization function of Matlab, wherein the coefficient of the over-determined equation is the same as the coefficient of a voltage-current equation. Specifically, after the over-determined equation is obtained in step S301, 7 coefficients of the over-determined equation can be obtained by solving the least square optimization function of Matlab.
And step S303, obtaining the fault distance according to the coefficient of the over-determined equation. Specifically, after 7 coefficients of the over-determined equation are obtained based on step S302, the relationship between the fault distance and the voltage-current equation coefficient can be obtained in the process of obtaining the voltage-current equation of a certain fault related to the ac bus by using KCL and KVL, and the voltage-current equation coefficient is the coefficient of the over-determined equation. Meanwhile, the relation between the fault distance and the equation coefficient can be obtained, and the transition resistance R can be obtainedfAssumed 0 mode resistance R after fault pointn0I.e. 0 mode inductance Ln0Wherein R isdc0Equivalent zero mode resistance, R, of inverter-side commutating transformern0The equivalent resistance from the fault point to the N-side system is specifically shown as follows:
Figure BDA0002585716580000131
preferably, the calculation formula for obtaining the fault distance according to the coefficients of the over-determined equation is as follows:
ρ＝x1
where ρ is the failure distance.
The method comprises the steps of obtaining an overdetermined equation with the equation number larger than a coefficient to be solved by bringing collected three-phase voltage of an alternating current bus, three-phase current of the alternating current bus and three-phase current of an inverter flowing to the alternating current bus into a voltage current equation, obtaining the coefficient of the overdetermined equation through a least square optimization function of Matlab, further obtaining a fault distance, and judging the type of the fault through the fault distance so as to enable a corresponding relay to act, realize protection on an alternating current circuit with a corresponding fault, realize simple calculation and improve the stability of an alternating current and direct current system.
And step S4, judging the fault type based on the fault distance, generating a breaker control signal according to the fault type, and controlling the inverter side breaker to execute corresponding actions to realize the protection of the single-phase alternating-current line. Specifically, the fault type can be determined by the fault distance obtained in step S3, and the protection device generates a circuit breaker control signal according to the fault type to control the inverter-side circuit breaker to perform a corresponding action, thereby implementing protection of the single-phase ac line.
Preferably, based on the fault distance, judge the fault type, protection device sends corresponding signal to contravariant side circuit breaker according to the fault type, and the circuit breaker carries out corresponding action based on the signal, includes:
if the fault distance is less than the full length of the single-phase alternating current line, the fault is an internal fault, the protection device sends a tripping signal to the inverter side breaker, and the breaker trips;
if the fault distance is larger than the total length of the single-phase alternating-current line, the fault is an out-of-area fault, and the protection device sends a locking signal to the inverter-side circuit breaker to lock the single-phase fault line.
Specifically, when the fault distance is less than the full length of the single-phase alternating-current line, the fault is an intra-area fault, the protection device sends a tripping signal to the inverter-side circuit breaker, and the circuit breaker trips; when the fault distance is larger than the total length of the single-phase alternating-current line, the protection device sends a locking signal to the inverter-side circuit breaker for an out-of-area fault, and locking of the single-phase fault line is achieved. And the single-phase alternating-current line is protected by comparing the fault distance with the full length of the single-phase alternating-current line.
The fault type is judged by comparing the fault distance with the full length of the single-phase alternating-current circuit, the protection device generates a circuit breaker control signal according to the fault type, and controls the circuit breaker on the inversion side to execute corresponding actions, so that the single-phase alternating-current circuit is protected, the judgment mode is simple and reliable, the accuracy is high, and the protection device is suitable for protecting an alternating-current and direct-current system rich in harmonic waves and non-periodic components.
Compared with the prior art, the single-phase alternating current line protection method for the alternating current and direct current system, provided by the embodiment, provides support and basis for constructing a voltage current equation of a certain fault related to the alternating current bus at the later stage by acquiring three-phase voltage and current information of the alternating current bus at the inversion side, obtains the voltage current equation of the certain fault related to the alternating current bus by adopting the KCL and KVL theorem, finally obtains the fault distance, and further judges the type of the fault according to the fault distance to realize the protection of the single-phase alternating current line.
As shown in FIG. 5, an AC-DC interconnection simulation model is built, a DC part is a +/-500 kV DC transmission system, and the voltage of an AC bus on an inverter side is 230 kV. The power transmission line connected with the alternating current bus at the inversion side comprises a line MN and a line MS, wherein the MN is set as a fault line. The total lengths of the circuits MN and MS are both 120km, wherein the positive sequence unit length resistor r1 is 0.1834 x 10-4 omega/M, the positive sequence unit length inductive reactance x1 is 0.263 x 10-3 omega/M, and the positive sequence unit length capacitive reactance c1 is 500M omega/M; the zero sequence unit length resistance r0 is 0.1417 × 10-3 Ω/km, the zero sequence unit length inductive reactance x0 is 0.6027 × 10-3 Ω/km, and the zero sequence unit length capacitive reactance C0 is 800M Ω M. The positive sequence impedance and the zero sequence impedance of the system S are respectively ZR1 ═ 4.477+ j59.913 Ω, and ZR0 ═ 2.0+ j6.37 Ω. The sampling frequency was 2 kHz.
And setting a 100 omega transition resistance ground fault at the position of 80km away from the inverter station on the AC line MN at 0.5 s. Because the differential equation solution is easily affected by higher harmonics, when the fault distance of simulation data is calculated, a second-order Butterworth filter is used for filtering signals, and the cut-off frequency is 100 Hz. The fault data was calculated by MATLAB with a data window of 10 ms. Based on the measured alternating current bus voltage and current data, the fault distance is obtained by using a least square optimization function and is shown in fig. 6, and the obtained transition resistance parameter is shown in fig. 7.
A phase A grounding fault is arranged at a position 120km away from an alternating current bus of the inverter station, namely the tail end of the line, and the resistance value of the transition resistor is set to be 100 omega. The calculation results of the failure distance are shown in fig. 8, and the calculation results of the transition resistance are shown in fig. 9. As can be seen from the figure, the protection method provided by the invention can identify the fault distance more accurately.
In order to further verify the accuracy of the protection method under different fault distances and different fault situations, different fault situations are set for simulation, and the simulation results are shown in table 1 below.
TABLE 1 simulation results for different fault distances and transition resistances
Figure BDA0002585716580000161
Since the ac line fault transition resistance in the power system does not exceed 300 ohms, the fault resistances in table 1 mainly have four resistances of 10 Ω, 100 Ω, 200 Ω and 300 Ω, and the fault distances are 25km, 50km, 75km and 120km of the line, respectively. As can be seen from table 1 above, the error of the ranging result in the present application is smaller than the fault distance, that is, the protection method of the present application can accurately identify the fault distance and the transition resistance in the single-phase high-resistance ground fault, and has higher accuracy.
In an embodiment of the present invention, a single-phase ac line protection device for an ac/dc system is disclosed, as shown in fig. 10. The method comprises the following steps: a data acquisition module 100 for acquiring the three-phase voltage u of the AC bus of the inverter sidema,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idcc(ii) a The protection calculation module 200 is used for obtaining a voltage current equation of a certain fault on the inversion side related to the alternating current bus by adopting a KCL theorem and a KVL theorem according to the zero-mode equivalent circuit of the alternating current-direct current interconnected power grid; a fault distance obtaining module 300 for obtaining a three-phase voltage u according to the AC busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation to obtain a fault distance; and the protection action module 400 is used for judging the fault type according to the fault distance, generating a circuit breaker control signal according to the fault type, and controlling the inverter side circuit breaker to execute corresponding actions so as to realize the protection of the single-phase alternating-current line.
The utility model provides a single-phase alternating current circuit protection device of alternating current-direct current system, three-phase voltage and current information through gathering contravariant side alternating current bus, construct certain trouble for the later stage and provide support and foundation in relation to the voltage current equation of alternating current bus, simultaneously, adopt KCL and KVL theorem to obtain the voltage current equation that certain trouble is in relation to alternating current bus, finally obtain the fault distance, and then judge the type of trouble through this fault distance, in order to realize the protection to single-phase alternating current circuit, the protection to alternating current-direct current system alternating current circuit has been realized, the stability ability of suitability and alternating current-direct current system has been improved.
Preferably, the protection calculation module obtains a voltage-current equation of a certain fault on the inverter side with respect to the ac bus as follows:
Figure BDA0002585716580000181
wherein the content of the first and second substances,
Figure BDA0002585716580000182
Figure BDA0002585716580000183
wherein z phase represents any fault phase of a, b and c phases, umzFor the z-phase voltage, i, of the AC busbar on the inverting sidemzFor the z-phase current, x, of the AC bus on the inverting sidejIs the coefficient of the voltage-current equation, j is 1,21、L11-mode resistance and inductance, k, of the AC line on the inverter sideRZero mode compensation for resistorsCoefficient, kR＝(R0-R1)/3R1，R0Zero mode resistance, k, for the inverting side AC lineLIs a zero-mode compensation coefficient, k, of the inductanceL＝(L0-L1)/3L1，L0Zero-mode inductance, i, for the inverting side AC linem0For zero-mode current i at the inverter side AC busbar protectiondc0Is the zero mode current component of the inverting side.
The voltage and current equation of a certain fault on the inversion side related to the alternating current bus is obtained through the protection calculation module, so that a foundation and a basis are provided for constructing an overdetermined equation in the later period, and the method is simple, easy to implement and easy to implement.
Preferably, the fault distance obtaining module performs the following process:
collecting three-phase voltage u of an inversion side alternating current bus in a time windowma,umb,umcThree-phase current i of AC busma,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccInputting the voltage current equation to obtain an overdetermined equation;
obtaining a coefficient of an over-determined equation based on a least square optimization function of Matlab, wherein the coefficient of the over-determined equation is the same as the coefficient of a voltage-current equation;
and obtaining the fault distance according to the coefficient of the over-determined equation.
Preferably, the calculation formula for obtaining the fault distance according to the coefficients of the over-determined equation is as follows:
ρ＝x1
where ρ is the failure distance.
The collected three-phase voltage of the alternating current bus, the collected three-phase current of the alternating current bus and the collected three-phase current of the inverter flowing to the alternating current bus are brought into a voltage current equation through a fault distance obtaining module, an overdetermined equation with the equation number larger than a coefficient to be solved can be obtained, the coefficient of the overdetermined equation is obtained through a least square optimization function of Matlab, and then the fault distance is obtained, and the type of the fault is judged through the fault distance, so that the corresponding relay acts, the protection of the corresponding fault alternating current circuit is realized, the calculation is simple, and the stability of an alternating current and direct current system is improved.
Preferably, the protection action module performs the following process:
if the fault distance is less than the full length of the single-phase alternating current line, the fault is an internal fault, the protection device sends a tripping signal to the inverter side breaker, and the breaker trips;
if the fault distance is larger than the total length of the single-phase alternating-current line, the fault is an out-of-area fault, and the protection device sends a locking signal to the inverter-side circuit breaker to lock the single-phase fault line.
The fault type is judged by comparing the fault distance with the full length of the single-phase alternating-current circuit through the protection action module, the protection device generates a circuit breaker control signal according to the fault type, the circuit breaker on the inversion side is controlled to execute corresponding actions, the single-phase alternating-current circuit is protected, the judgment mode is simple and reliable, the accuracy is high, and the protection device is suitable for protection of an alternating-current and direct-current system with rich harmonic waves and non-periodic components.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (6)

1. A single-phase alternating current line protection method of an alternating current and direct current system is characterized by comprising the following steps:
three-phase voltage u of alternating current bus on inversion side is collectedma,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idcc；
Based on the AC-DC interconnected power grid zero-mode equivalent circuit, adopting a KCL theorem and a KVL theorem to obtain a voltage-current equation of a certain fault on an inverter side relative to an AC bus; the voltage and current equation of a certain fault on the inversion side related to the alternating current bus is as follows:
Figure FDA0003210912970000011
wherein the content of the first and second substances,
Figure FDA0003210912970000012
Figure FDA0003210912970000013
wherein z phase represents any fault phase of a, b and c phases, umzFor the z-phase voltage, i, of the AC busbar on the inverting sidemzFor the z-phase current, x, of the AC bus on the inverting sidejIs the coefficient of the voltage-current equation, j is 1,21、L11-mode resistance and inductance, k, of the AC line on the inverter sideRIs a zero-mode compensation coefficient, k, of the resistanceR＝(R0-R1)/3R1，R0Zero mode resistance, k, for the inverting side AC lineLIs a zero-mode compensation coefficient, k, of the inductanceL＝(L0-L1)/3L1，L0Zero-mode inductance, i, for the inverting side AC linem0For zero-mode current i at the inverter side AC busbar protectiondc0Is a zero-mode current component of the inversion side; the AC-DC interconnected power grid zero-mode equivalent circuit is obtained according to the topological structure characteristics of the AC-DC interconnected system;
three-phase voltage u based on alternating current busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation to obtain a fault distance;
judging the fault type based on the fault distance;
generating a breaker control signal according to the fault type, and controlling the inverter side breaker to execute corresponding actions to realize the protection of the single-phase alternating-current line; the method comprises the following steps:
if the fault distance is less than the full length of the single-phase alternating-current line, the fault is an intra-area fault, the protection device sends a tripping signal to the inverter side breaker, and the breaker trips;
if the fault distance is larger than the total length of the single-phase alternating-current line, the fault is an out-of-area fault, and the protection device sends a locking signal to the inverter-side circuit breaker to lock the single-phase fault line.
2. A single-phase ac line protection method according to claim 1, characterized in that the three-phase voltage u based on the ac busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation, obtaining a fault distance, comprising:
collecting three-phase voltage u of an inversion side alternating current bus in a time windowma,umb,umcThree-phase current i of AC busma,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccInputting the voltage current equation to obtain an overdetermined equation;
obtaining a coefficient of the over-determined equation based on a least square optimization function of Matlab, wherein the coefficient of the over-determined equation is the same as the coefficient of the voltage-current equation;
and obtaining the fault distance according to the coefficient of the over-determined equation.
3. The single-phase ac line protection method according to claim 2, wherein the calculation formula for obtaining the fault distance from the coefficients of the over-determined equation is:
ρ＝x1
where ρ is the failure distance.
4. A single-phase AC line protection system for an AC/DC system, comprising:
the data acquisition module is used for acquiring the three-phase voltage u of the AC bus on the inversion sidema,umb,umcThree-phase current ima,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idcc；
The protection calculation module is used for obtaining a voltage current equation of a certain fault on the inversion side related to the alternating current bus by adopting a KCL theorem and a KVL theorem according to the zero-mode equivalent circuit of the alternating current-direct current interconnected power grid; the voltage and current equation of a certain fault on the inversion side related to the alternating current bus is as follows:
Figure FDA0003210912970000031
wherein the content of the first and second substances,
Figure FDA0003210912970000032
Figure FDA0003210912970000033
wherein z phase represents any fault phase of a, b and c phases, umzFor the z-phase voltage, i, of the AC busbar on the inverting sidemzFor the z-phase current, x, of the AC bus on the inverting sidejIs the coefficient of the voltage-current equation, j is 1,21、L11-mode resistance and inductance, k, of the AC line on the inverter sideRIs a zero-mode compensation coefficient, k, of the resistanceR＝(R0-R1)/3R1，R0Zero mode resistance, k, for the inverting side AC lineLIs a zero-mode compensation coefficient, k, of the inductanceL＝(L0-L1)/3L1，L0Zero-mode inductance, i, for the inverting side AC linem0For zero-mode current i at the inverter side AC busbar protectiondc0Is a zero-mode current component of the inversion side; zero mode of alternating current-direct current interconnected power gridThe equivalent circuit is obtained according to the topological structure characteristics of the AC-DC interconnection system;
a fault distance obtaining module for obtaining the three-phase voltage u of the AC busma,umb,umcThree-phase current i of AC busma,imb,imcThree-phase current i of inverter flowing to alternating current busdca,idcb,idccAnd a voltage current equation to obtain a fault distance;
the protection action module is used for judging the fault type according to the fault distance, generating a circuit breaker control signal according to the fault type, and controlling the circuit breaker on the inversion side to execute corresponding actions so as to realize the protection of the single-phase alternating-current line; the method comprises the following steps:
if the fault distance is less than the full length of the single-phase alternating-current line, the fault is an intra-area fault, the protection device sends a tripping signal to the inverter side breaker, and the breaker trips;
if the fault distance is larger than the total length of the single-phase alternating-current line, the fault is an out-of-area fault, and the protection device sends a locking signal to the inverter-side circuit breaker to lock the single-phase fault line.
5. The single-phase ac line protection system according to claim 4, wherein the fault distance obtaining module performs the following procedure:
collecting three-phase voltage u of an inversion side alternating current bus in a time windowma,umb,umcThree-phase current i of AC busma,imb,imcAnd three-phase current i of inverter flowing to AC busdca,idcb,idccInputting the voltage current equation to obtain an overdetermined equation;
obtaining a coefficient of the over-determined equation based on a least square optimization function of Matlab, wherein the coefficient of the over-determined equation is the same as the coefficient of the voltage-current equation;
and obtaining the fault distance according to the coefficient of the over-determined equation.
6. The single-phase ac line protection system of claim 5, wherein the calculation formula for obtaining the fault distance from the coefficients of the over-determined equation is:
ρ＝x1
where ρ is the failure distance.
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