CN109286202B - Large-scale inversion type power supply grid-connected tie line current differential protection method, device and system - Google Patents
Large-scale inversion type power supply grid-connected tie line current differential protection method, device and system Download PDFInfo
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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
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
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Abstract
The invention discloses a large-scale inversion type power supply grid-connected tie line current differential protection method, device and system based on negative sequence components, comprising S1 collecting the current flowing through the protection 1 and protection 2 at the two ends of a tie line PQ, and calculating the corresponding current phasor; s2, respectively calculating positive sequence, negative sequence and zero sequence components of current phasors at two ends of the tie line; s3, respectively calculating the synthetic currents of the system side and the inversion type power supply side to highlight the negative sequence current difference at the two ends of the tie line; s4 calculating a differential ratio coefficient; s5 calculating the differential current of each phase line in three phases
S6 setting protection action threshold KrelAnd split-phase current differential protection setting value IsetWhen C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the link area is in fault; and S7, if the judgment result is that the inside of the tie line area has a fault, the protection sends out a trip signal to isolate the fault area of the tie line from the system. The invention can reliably distinguish the internal and external faults and the normal operation condition of the region and overcome the problem of low sensitivity of the traditional current differential protection.
Description
Technical Field
The invention relates to the technical field of relay protection of power systems, in particular to a large-scale inversion type power supply grid-connected tie line current differential protection method, device and system.
Background
Inverter-interface power supplies (IIG) represented by photovoltaic cells and permanent magnet direct-drive wind generators are being incorporated into power grids on a large scale. Compared with the traditional alternating current synchronous generator set, the inverter type power supply mainly comprises power electronic devices, on one hand, the power electronic devices have weak overvoltage and overcurrent resistance, on the other hand, the inverter type power supply has short transient response time and has the characteristics of nonlinearity and strong coupling, the fault characteristics of the inverter type power supply are mainly determined by control strategies during fault, and the fault characteristics of the inverter type power supply and the fault characteristics of the traditional power supply have obvious difference due to the flexible fault control strategies. The power grid fault analysis method, the protection principle and the protection setting method based on the fault characteristics of the traditional alternating current synchronous generator have adaptability problems.
The relay protection is used as a first defense line for the safe and stable operation of the power system, the reduction of the protective performance of the sending-out tie line of the inverter type power supply poses great threat to the safety of the power grid, and the problem of the deterioration of the protective performance also becomes a key problem for restricting the development of the inverter type power supply.
The current large-scale inverter type power supply output connecting line mainly adopts longitudinal distance protection and current differential protection as main protection. The pilot distance protection judges the internal and external faults through the distance protection at two ends of a connecting line, but the protection does not tolerate the transition resistance, protects the measured impedance to be easily influenced by the fault current characteristic of the inverter power supply during the fault, and cannot reflect the real fault distance. The traditional current differential protection has absolute selectivity on faults inside and outside a zone, but is influenced by the fault current limiting characteristic of a large-scale inverter type power supply, the traditional current differential protection scheme based on the full fault current has the problem of insufficient sensitivity, and the protection may be refused to the faults in a tie line zone.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: based on the fault current characteristic of an inverse variant power supply under a positive sequence component control strategy, a large-scale inverse power supply grid-connected tie line current differential protection method based on a negative sequence component is provided, the problems that the traditional current differential protection sensitivity of an inverse power supply tie line is low and the protection is possible to have in-region fault rejection under the fault current-limiting characteristic of the large-scale inverse power supply are solved, and the grid-connected safe and reliable operation of the large-scale inverse power supply is guaranteed.
The technical scheme of the invention is as follows:
in a first aspect, the invention provides a large-scale inverse power supply grid-connected tie line current differential protection method based on a negative sequence component, wherein a power grid comprises a bus P, a bus Q and a tie line PQ between the bus P and the bus Q, an inverse power supply is connected to the opposite side of the tie line PQ system side through a main transformer, and the system side and the inverse power supply side of the tie line PQ are respectively provided with a protection 1 and a protection 2;
the method comprises the following steps:
s1, respectively collecting the current flowing through two ends of the connecting line PQ through the protection 1 and the protection 2, and calculating corresponding current phasors;
s2, respectively calculating the positive sequence, negative sequence and zero sequence components of the current flowing through the two ends of the tie line through protection 1 and protection 2 based on the current phasor obtained in S1;
s3, based on the obtained current components of the system side and the inversion type power supply side from S2, reducing the positive sequence current and the zero sequence current according to a preset sequence current scaling coefficient, adding the reduced positive sequence current and zero sequence current with the negative sequence current, and respectively calculating to obtain the synthetic currents of the system side and the inversion type power supply side;
s4, calculating the ratio of the inverter power supply side synthetic current to the system side synthetic current, and using the ratio as a differential ratio coefficient Cdiff；
S5, calculating the differential current of each phase line on the connecting line PQ in the three phases respectively
Wherein the content of the first and second substances,
and
are respectively a tie line
Current phasors at the system side and the inverter type power supply side on the phase;
s6, according to the preset protection action threshold KrelAnd split-phase current differential protection setting value IsetBased on the differential ratio coefficient CdiffAnd differential currents of the phases
The following judgments were made:
when C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the inside of the tie line area is in fault, otherwise, judging that the outside of the tie line area is in fault or the system is in a normal operation state;
and S7, executing protection action according to the judgment result of S6, and if the judgment result is that the inside of the tie line area is in fault, sending a trip signal by protection to isolate the fault area of the tie line from the system.
Preferably, in S1, the current phasor flowing across the tie line PQ is calculated by a fourier algorithm. Fourier algorithms are prior art.
Preferably, in S2, based on the current phasor obtained in S1, positive-sequence, negative-sequence, and zero-sequence components of the current phasor are calculated by a symmetric component method. Symmetrical component method is prior art, for the current phasor flowing through protection 1
And the current phasor flowing through the protection 2
The current flowing through the protection 1, i.e. each sequence component of the system side current, can be obtained by using the symmetrical component method as
And
the current flowing through the protection 2, i.e., the inverter type power supply side current, has the sequence components of
And
preferably, in S3, the resultant current calculation formula is:
wherein, I is the synthesized current,
the current positive sequence, negative sequence and zero sequence components are respectively, and k is a sequence current scaling coefficient. In addition, in the calculation process of the synthetic current, other algorithms can be adopted to respectively reduce the positive sequence current and the zero sequence current so as to achieve the purpose of highlighting the negative sequence current difference.
Preferably, based on the implementation of equation (1), in S3, the value of the sequence current scaling coefficient k ranges from 0.1 to 0.2, and is an empirical value, so that the effect of the positive sequence current component and the zero sequence current component in the fault full current can be effectively weakened, the negative sequence current difference at the two ends of the tie line is highlighted, and the reliability of the differential ratio coefficient criterion is improved.
From equation (1), the resulting system-side current is:
the inverse power supply side synthesized current is as follows:
preferably, in S4, the differential ratio coefficient CdiffThe calculation formula of (2) is as follows:
wherein IIIGAnd IsysThe synthesized currents of the inverter type power supply side and the system side, respectively.
The differential ratio coefficient calculation method based on equation (4) in S6 is the protection operation threshold KrelIs 1.
Based on equation (4), more preferably, in S6, the protection operation threshold KrelThe value range of (A) is 0.8-0.85. The judgment result of the protection logic can be more reliable.
In a second aspect, the invention further discloses a large-scale inverse power supply grid-connected tie line current differential protection device based on the negative sequence component, wherein a power grid comprises a bus P, a bus Q and a tie line PQ between the bus P and the bus Q, an inverse power supply is connected to the opposite side of the tie line PQ system side through a main transformer, and the system side and the inverse power supply side of the tie line PQ are respectively provided with a protection 1 and a protection 2;
the current differential protection device includes:
the current acquisition and calculation module is used for respectively acquiring the currents flowing through two ends of the connecting line PQ through the protection 1 and the protection 2 and calculating corresponding current phasors;
the current component calculation module is used for calculating the positive sequence, negative sequence and zero sequence components of the current flowing through the two ends of the tie line through the protection 1 and the protection 2 respectively based on the obtained current phasors;
the synthetic current calculation module is used for reducing the positive sequence current and the zero sequence current according to a preset sequence current scaling coefficient on the basis of the obtained current components of each sequence of the system side and the inversion type power supply side, adding the reduced positive sequence current and zero sequence current with the negative sequence current, and calculating synthetic currents of the system side and the inversion type power supply side respectively;
a differential ratio coefficient calculation module for calculating the ratio of the inverter type power supply side synthetic current to the system side synthetic current as a differential ratio coefficient Cdiff；
A differential current calculating module for calculating the differential current of each phase line on the connecting line PQ in three phases
Wherein the content of the first and second substances,
and
are respectively a tie line
Current phasors at the system side and the inverter type power supply side on the phase;
a protection logic judgment module for judging the protection action threshold K according to the preset protection action thresholdrelAnd split-phase current differential protection setting value IsetBased on the differential ratio coefficient CdiffAnd differential currents of the phases
The following judgments were made:
when C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the inside of the tie line area is in fault, otherwise, judging that the outside of the tie line area is in fault or the system is in a normal operation state;
and the protection action execution module executes a protection action according to the protection logic judgment result: and if the judgment result is that the interconnection line has a fault in the area, the protection sends out a tripping signal to isolate the interconnection line fault area from the system.
In a third aspect, the present invention further provides a system for the large-scale inverse power supply grid-connected tie line current differential protection method based on the negative sequence component in the first aspect, which includes a network interface, a memory and a processor, wherein:
the network interface is used for receiving and sending signals in the process of sending and receiving information between the system and other external network elements;
a memory for storing computer program instructions executable on the processor;
the processor is configured to execute the steps of the large-scale inverter-type power supply grid-connected tie line current differential protection method according to any one of the first aspect when the computer program instructions are executed.
Advantageous effects
1) According to the invention, the effect of the positive sequence current component and the zero sequence current component in the fault full current is weakened by utilizing the difference of the negative sequence current components at the two ends of the tie line under the condition of internal and external faults of the tie line area, so that the protection sensitivity can be improved, the protection can correctly act under different operation modes, transition resistances, fault positions and the length of the tie line, and the safe and stable operation of the large-scale inversion type power supply tie line can be ensured;
2) the differential ratio coefficient criterion is combined with the traditional current differential protection criterion to form redundant protection configuration, so that the reliability of protection action under three-phase symmetric faults is improved;
in conclusion, the invention ensures that the tie line protection can reliably distinguish the internal and external faults and the normal operation condition of the zone, overcomes the problem of low sensitivity of the traditional current differential protection and has good application prospect.
Drawings
FIG. 1 is a schematic diagram of a large-scale inverter type power supply access power grid structure;
FIG. 2 is a flow chart of a method according to an embodiment of the present invention.
Detailed Description
The following further description is made in conjunction with the accompanying drawings and the specific embodiments.
Referring to fig. 1, a schematic diagram of a large-scale inverter type power supply access grid is shown in fig. 1. The power grid comprises a bus P, a bus Q and a connecting line PQ between the bus P and the bus Q, the inverter type power supply is connected to the opposite side of the system side of the connecting line PQ through a step-up main transformer, and the system side and the inverter type power supply side of the connecting line PQ are respectively provided with a protection 1 and a protection 2 to form current differential protection of the connecting line PQ. The positive direction of current is shown by the arrow in fig. 1, and if a fault on line PQ occurs, the fault is judged to be an in-zone fault, and if a fault occurs in an area outside line PQ, the protection is judged to be an out-of-zone fault. The inverter type power supply adopts a positive sequence component control strategy during a fault.
Example 1
Referring to fig. 2, the present embodiment is a negative sequence component-based large-scale inverter-type power supply grid-connected tie line current differential protection method, including:
s1, respectively collecting the current flowing through the two ends of the connecting line PQ through the protection 1 and the protection 2, and calculating corresponding current phasors by utilizing a Fourier algorithm
And
s2, obtaining current phasor based on S1
And
respectively calculating positive sequence, negative sequence and zero sequence components of currents flowing through two ends of the tie line through protection 1 and protection 2 by using a symmetrical component method; wherein the current flowing through the protection 1, namely the system side current, has sequence components of
And
the current flowing through the protection 2, i.e., each sequence component of the inverter-type power supply side current is
And
s3, based on the obtained current components of the system side and the inversion type power supply side from S2, reducing the positive sequence current and the zero sequence current according to a preset sequence current scaling coefficient, adding the reduced positive sequence current and zero sequence current with the negative sequence current, and respectively calculating to obtain the synthetic currents of the system side and the inversion type power supply side;
in this embodiment, the calculation formula of the synthesized current is:
wherein, I is the synthesized current,
respectively a positive sequence component, a negative sequence component and a zero sequence component of the current, and k is a sequence current scaling coefficient;
the value range of the sequence current scaling coefficient k is 0.1-0.2, the value of the sequence current scaling coefficient k is an empirical value, the effects of a positive sequence current component and a zero sequence current component in fault full current can be effectively weakened, the negative sequence current difference at two ends of a connecting line is highlighted, and the reliability of differential ratio coefficient criterion is improved;
from equation (1), the resulting system-side current is:
the inverse power supply side synthesized current is as follows:
s4, calculating a differential ratio coefficient CdiffComprises the following steps:
s5, calculating the differential current of each phase line on the connecting line PQ in the three phases respectively
Wherein the content of the first and second substances,
and
are respectively a tie line
Current phasors at the system side and the inverter type power supply side on the phase;
s6, setting protection action threshold KrelAnd split-phase current differential protection setting value IsetBased on the differential ratio coefficient CdiffAnd differential currents of the phases
And (4) carrying out protection logic judgment:
when C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the inside of the tie line area is in fault, otherwise, judging that the outside of the tie line area is in fault or the system is in a normal operation state;
protective action threshold KrelThe value can be simply set to 1 and can be taken between 0.8 and 0.85, so that the judgment result of the protection logic is more reliable.
And S7, executing protection action according to the judgment result of S6, and if the judgment result is that the inside of the tie line area is in fault, sending a trip signal by protection to isolate the fault area of the tie line from the system.
According to the large-scale inverse power supply grid-connected tie line current differential protection method based on the negative sequence component, the difference of the negative sequence current components at two ends of the tie line is utilized under the condition of internal and external faults of the tie line area, the effect of the positive sequence current component and the zero sequence current component in the fault full current is weakened, the protection sensitivity can be improved, the protection can correctly act under different operation modes, transition resistances, fault positions and the length of the tie line, and the safe and stable operation of the large-scale inverse power supply grid-connected tie line can be ensured.
Meanwhile, the differential ratio coefficient criterion and the traditional current differential protection criterion are combined to form redundant protection configuration, so that the reliability of protection action under three-phase symmetric faults is improved.
Example 2
Based on the same inventive concept as that of embodiment 1, the present embodiment is a negative-sequence-component-based large-scale inverter-type power supply grid-connected link current differential protection device, including:
the current acquisition and calculation module is used for respectively acquiring the currents flowing through two ends of the connecting line PQ through the protection 1 and the protection 2 and calculating corresponding current phasors;
the current component calculation module is used for calculating the positive sequence, negative sequence and zero sequence components of the current flowing through the two ends of the tie line through the protection 1 and the protection 2 respectively based on the obtained current phasors;
the synthetic current calculation module is used for reducing the positive sequence current and the zero sequence current according to a preset sequence current scaling coefficient on the basis of the obtained current components of each sequence of the system side and the inversion type power supply side, adding the reduced positive sequence current and zero sequence current with the negative sequence current, and calculating synthetic currents of the system side and the inversion type power supply side respectively;
the resultant current calculation formula may be:
wherein, I is the synthesized current,
respectively a positive sequence component, a negative sequence component and a zero sequence component of the current, and k is a sequence current scaling coefficient; the value range of the sequence current scaling coefficient k is 0.1-0.2.
A differential ratio coefficient calculation module for calculating the ratio of the inverter type power supply side synthetic current to the system side synthetic current as a differential ratio coefficient Cdiff：
Wherein IIIGAnd IsysRespectively the synthetic currents of the inverter type power supply side and the system side;
a differential current calculating module for calculating the differential current of each phase line on the connecting line PQ in three phases
Wherein the content of the first and second substances,
and
are respectively a tie line
Current phasors at the system side and the inverter type power supply side on the phase;
a protection logic judgment module for judging the protection action threshold K according to the preset protection action thresholdrelAnd split-phase current differential protection setting value IsetBased on the differential ratio coefficient CdiffAnd differential currents of the phases
And (4) carrying out protection logic judgment:
when C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the inside of the tie line area is in fault, otherwise, judging that the outside of the tie line area is in fault or the system is in a normal operation state;
protective action threshold KrelThe value can be simply set to 1 and can be taken between 0.8 and 0.85, so that the judgment result of the protection logic is more reliable;
and the protection action execution module executes a protection action according to the protection logic judgment result: and if the judgment result is that the interconnection line has a fault in the area, the protection sends out a tripping signal to isolate the interconnection line fault area from the system.
Example 3
Based on the same inventive concept as that in embodiment 1, this embodiment is a system of the current differential protection method for the large-scale inverse power supply grid-connected tie line based on the negative sequence component in the first aspect, and the system includes a network interface, a memory, and a processor, where:
the network interface is used for receiving and sending signals in the process of sending and receiving information between the system and other external network elements;
a memory for storing computer program instructions executable on the processor;
the processor is used for executing the steps of the negative sequence component-based large-scale inverter type power grid-connected tie line current differential protection method according to any one of the first aspect when the computer program instructions are executed.
In summary, the present invention fully utilizes the significant difference existing in the negative sequence component of the current flowing through the inverter type power supply tie line under the control of the positive sequence component during the intra-area fault, introduces the sequence current scaling factor, respectively calculates the synthetic currents of the system side and the inverter type power supply side at the two ends of the tie line, and forms the differential ratio factor required by the method for discriminating the intra-area fault and the external fault by the ratio of the synthetic currents of the inverter type power supply side and the system side. The coefficient has good judgment boundary for the faults and normal operation conditions inside and outside the area, and the protection action is reliable. The protection method fully utilizes the difference between the current negative sequence components at the two sides of the tie line, overcomes the problem that the protection is rejected when the traditional current differential protection fails in a region under the influence of the fault current limiting characteristic of an inverter type power supply, greatly improves the sensitivity of the protection method, and has good application prospect on ensuring the safe and reliable operation of large-scale inverter type power supply grid connection, particularly on the inverter type power supply grid connection tie line adopting a positive sequence component control strategy during the fault.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A large-scale inversion type power supply grid-connected tie line current differential protection method is characterized in that a power grid comprises a bus P, a bus Q and a tie line PQ between the bus P and the bus Q, and an inversion type power supply is connected to the opposite side of the tie line PQ system side through a main transformer; the method is characterized in that: a system side and an inverter type power supply side of the connecting line PQ are respectively provided with a protection 1 and a protection 2;
the method comprises the following steps:
s1, respectively collecting the current flowing through two ends of the connecting line PQ through the protection 1 and the protection 2, and calculating corresponding current phasors;
s2, respectively calculating the positive sequence, negative sequence and zero sequence components of the current flowing through the two ends of the connecting line PQ through the protection 1 and the protection 2 based on the current phasor obtained in the step S1;
s3, based on the obtained current components of the system side and the inversion type power supply side from S2, reducing the positive sequence current and the zero sequence current according to a preset sequence current scaling coefficient, adding the reduced positive sequence current and zero sequence current with the negative sequence current, and respectively calculating to obtain the synthetic currents of the system side and the inversion type power supply side;
s4, calculating the ratio of the inverter power supply side synthetic current to the system side synthetic current, and using the ratio as a differential ratio coefficient Cdiff；
S5, calculating the differential current of each phase line on the connecting line PQ in the three phases respectively
Wherein the content of the first and second substances,
and
are respectively a tie line
Current phasors at the system side and the inverter type power supply side on the phase;
s6, according to the preset protection action threshold KrelAnd split-phase current differential protection setting value IsetBased on the differential ratio coefficient CdiffAnd differential currents of the phases
The following judgments were made:
when C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the inside of the tie line area is in fault, otherwise, judging that the outside of the tie line area is in fault or the system is in a normal operation state;
and S7, executing protection action according to the judgment result of S6, and if the judgment result is that the inside of the tie line area is in fault, sending a trip signal by protection to isolate the fault area of the tie line from the system.
2. The method of claim 1, further comprising: at S1, the current phasor flowing through both ends of the connecting line PQ is calculated by a fourier algorithm.
3. The method of claim 1, further comprising: in S2, the positive, negative and zero sequence components are calculated by a symmetric component method based on the current phasor obtained in S1.
4. The method of claim 1, further comprising: in S3, the resultant current calculation formula is:
wherein, I is the synthesized current,
the current positive sequence, negative sequence and zero sequence components are respectively, and k is a sequence current scaling coefficient.
5. The method of claim 4, wherein: the value range of the sequence current scaling coefficient k is 0.1-0.2.
6. The method of claim 1, further comprising: in S4, the differential ratio coefficient CdiffThe calculation formula of (2) is as follows:
wherein IIIGAnd IsysThe synthesized currents of the inverter type power supply side and the system side, respectively.
7. The method of claim 6, wherein: in S6, protection operation threshold KrelIs 1.
8. The method of claim 6, wherein: in S6, protection operation threshold KrelThe value range of (A) is 0.8-0.85.
9. A large-scale inversion type power supply grid-connected tie line current differential protection device comprises a bus P, a bus Q and a tie line PQ between the bus P and the bus Q, wherein an inversion type power supply is connected to the opposite side of the tie line PQ through a main transformer, and the system side and the inversion type power supply side of the tie line PQ are respectively provided with a protection 1 and a protection 2; the method is characterized in that: the current differential protection device includes:
the current acquisition and calculation module is used for respectively acquiring the currents flowing through two ends of the connecting line PQ through the protection 1 and the protection 2 and calculating corresponding current phasors;
the current component calculation module is used for calculating the positive sequence, negative sequence and zero sequence components of the current flowing through the two ends of the tie line through the protection 1 and the protection 2 respectively based on the obtained current phasors;
the synthetic current calculation module is used for reducing the positive sequence current and the zero sequence current according to a preset sequence current scaling coefficient on the basis of the obtained current components of each sequence of the system side and the inversion type power supply side, adding the reduced positive sequence current and zero sequence current with the negative sequence current, and calculating synthetic currents of the system side and the inversion type power supply side respectively;
a differential ratio coefficient calculation module for calculating the ratio of the inverter type power supply side synthetic current to the system side synthetic current as a differential ratio coefficient Cdiff；
A differential current calculating module for calculating the differential current of each phase line on the connecting line PQ in three phases
Wherein the content of the first and second substances,
and
are respectively a tie line
Current phasors at the system side and the inverter type power supply side on the phase;
a protection logic judgment module for judging the protection action threshold K according to the preset protection action thresholdrelAnd split-phase current differential protection setting value IsetBased on the differential ratio coefficient CdiffAnd differential currents of the phases
The following judgments were made:
when C is satisfieddiff≤KrelOr is or
If any condition is met, judging that the inside of the tie line area is in fault, otherwise, judging that the outside of the tie line area is in fault or the system is in a normal operation state;
and the protection action execution module executes a protection action according to the protection logic judgment result: and if the judgment result is that the interconnection line has a fault in the area, the protection sends out a tripping signal to isolate the interconnection line fault area from the system.
10. A system for the large-scale inverter type power supply grid-connected tie line current differential protection method according to any one of claims 1 to 8, characterized in that: comprising a network interface, a memory, and a processor, wherein:
the network interface is used for receiving and sending signals in the process of sending and receiving information between the system and other external network elements;
a memory for storing computer program instructions executable on the processor; the processor is used for executing the steps of the large-scale inverter type power grid-connected tie line current differential protection method according to any one of claims 1 to 8 when the computer program instructions are executed.
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