Fault area positioning method for distribution network containing photovoltaic power generation based on wide area protection system

Abstract

The present invention discloses a method for locating the fault area of ​​a photovoltaic power distribution network based on a wide area protection system, including the following steps: when a fault occurs, determine the search direction of the fault area, including: determine the size of the comprehensive amplitude of the current of the three-branch circuit; determine the positive direction and reverse direction of the fault area search according to the comparison result of the comprehensive amplitude of the current; locate the fault area including the following algorithms: construct a network association description matrix; calculate the fault search reverse direction matrix; revise the network association description matrix according to the search reverse direction matrix to obtain the fault discrimination matrix P; analyze and discriminate the fault occurrence area. The matrix algorithm of the fault area positioning part proposed in the method is adaptable to the constantly changing network topology structure, does not distinguish between the intermediate nodes and edge nodes of the network topology structure, and can clearly distinguish these two types of nodes in the judgment criteria, has no matrix multiplication operation, has a small amount of operation, and has stability and versatility.

Description

Technical Field

[0001] The invention belongs to the field of power network fault positioning, and in particular relates to a method for positioning a fault area of ​​a photovoltaic power distribution network based on a wide area protection system. Background Art

[0002] Distributed power sources with low pollution and low loss will have greater room for development. When more distributed power sources are connected to the distribution network, the distribution network changes from a single-power radial network to a complex multi-power structure, and the power grid flow also changes accordingly. This change brings difficulties to fault location. Therefore, the distribution network fault location method needs to be more stable and universal.

[0003] At present, there are three fault location algorithms: traveling wave method, artificial intelligence algorithm and matrix algorithm. The traveling wave method is only applicable to feeders with a single material and few branches, and is not very practical; the artificial intelligence algorithm is complex in theory and has a large amount of calculation, and its application in fault location is not mature enough; the matrix algorithm based on matrix analysis and processing has a simple principle and a small amount of calculation, and is widely used in actual fault location.

[0004] The fault location matrix algorithm based on distribution network automation determines the fault location by detecting the overcurrent direction through the feeder terminal unit (FTU). This matrix algorithm does not require normalization processing, no multiplication operation, and the judgment principle is simple and intuitive. However, the current distribution network feeder section switch is only equipped with A-phase and C-phase current transformers, and no voltage transformer is installed, so the overcurrent direction is difficult to detect.

[0005] The new current protection system applies wide-area protection to the current protection of the distribution network containing distributed power sources. The fault area location uses the comprehensive current amplitude as the basis for judgment, and the fault section location uses the phase relationship between currents as the basis for judgment, which overcomes the disadvantage that the overcurrent direction is difficult to detect. However, in the matrix algorithm of the fault area search part, it is necessary to master the node information in advance, and use different matrix revision methods for the intermediate nodes and edge nodes, and the revision process is relatively cumbersome. Summary of the invention

[0006] In order to solve the deficiencies of the prior art, the present invention aims to provide a method for locating the fault area of ​​a photovoltaic power distribution network based on a wide area protection system. The matrix algorithm of the fault area locating part proposed in the method does not need to master the node information in advance. The current information is collected and processed by IED and the search direction is determined to form a fault search positive direction matrix and a reverse direction matrix. The network association description matrix is ​​revised according to the search reverse direction matrix. The algorithm is adaptable to the ever-changing network topology structure, and can clearly distinguish the two types of nodes in the criterion. There is no matrix multiplication operation, the amount of operation is small, and it has stability and versatility.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The method for locating fault areas of a photovoltaic power distribution network based on a wide area protection system comprises the following steps:

[0009] 1) When a fault occurs, the search direction of the fault area is determined, including:

[0010] 1-3) Determine the magnitude of the comprehensive current amplitude of the three-branch circuit;

[0011] 1-4) According to the comparison result of the comprehensive current amplitude, determine the positive direction and reverse direction of the fault area search;

[0012] 2) Locating the fault area includes the following algorithms:

[0013] 2-1) Construct a network association description matrix D to describe the neighbor relationship of the intelligent electronic devices IED at each section switch;

[0014] 2-2) The fault search direction is stored in the form of a matrix, the positive direction of the fault search is Z, and the fault search reverse direction matrix F=DZ is calculated;

[0015] 2-3) The network association description matrix D is revised according to the search reverse direction matrix F, and the revised result is the fault discrimination matrix P;

[0016] 2-4) Analyze the fault discrimination matrix P to identify the fault occurrence area.

[0017] Step 1-1) Comparison of the comprehensive amplitudes of the three-branch currents during a fault includes:

[0018] The comprehensive current amplitude is the sum of the positive sequence component amplitude and the negative sequence component amplitude of the fault current, that is,

[0019]

[0020] Assume S a The impedance of the system is Z sa =|Z sa |∠α, impedance Z of DG1 ga =|Z ga |∠β, when fault occurs, the voltage of DG1 is U1=U1∠γ, ∠α and ∠β are impedance angles; ∠γ is the voltage phase of DG1, which is a parameter in the sinusoidal alternating current expression and is a known quantity that can be measured;

[0021] S a The positive sequence component of the system side branch is

[0022]

[0023] The positive sequence component of DG1 branch is

[0024]

[0025] The positive sequence component of the branch current pointing to the fault point is

[0026]

[0027] According to the cosine theorem, we can get

[0028]

[0029] Since the transient reactance of the generator is inductive, the impedance of the system and the line is also inductive, so |α-β|≈0, that is,

[0030]

[0031]

[0032] The positive sequence amplitude of the current in the branch pointing to the fault point is the largest;

[0033] The same can be said

[0034]

[0035]

[0036] The negative sequence amplitude of the current in the branch pointing to the fault point is the largest; then the comprehensive amplitude of the current in the branch pointing to the fault point is the largest.

[0037] Step 1-2) specifically includes: based on the comparison of the comprehensive amplitudes of the currents in the three-branch circuits, the current direction of the branch with the largest amplitude is the positive direction of the fault area search, and the direction opposite to the positive search direction is the reverse direction of the fault area search.

[0038] Step 2-1) The construction of the network association description matrix includes:

[0039] A network association description matrix D is stored in the protection device, and the IEDs at the feeder nodes are numbered. Assuming there are n IEDs in total, an n×n square matrix D can be constructed, which is defined as follows:

[0040] If the i-th and j-th IEDs are adjacent, denoted as IEDi and IEDj, then the corresponding element D in the network association description matrix D is ij =1,D ji =1; if IEDi and IEDj are not adjacent, then the corresponding element D in the network association description matrix D ij =0,D ji =0; all D in the matrix ii =0, that is, all elements on the diagonal of the network association description matrix D are 0.

[0041] Step 2-2) The calculation of the fault search reverse matrix includes:

[0042] Each IED samples and compares the comprehensive current amplitude of the three branches, determines the fault search direction, communicates with the centralized controller, and stores the fault search direction in the form of a matrix, where the positive direction of the fault search is Z and the negative direction of the fault search is F;

[0043] IED A is used to sample and compare the comprehensive current amplitudes of the three branches, and IED B is used to sample and compare the current phases of the two branches;

[0044] The current comprehensive amplitudes of the three branches of each IED A are compared one by one. For IEDi, if the fault search direction is determined to be the adjacent IEDj after comparing the current comprehensive amplitudes, the element Z in the jth column of the i-th row in the positive direction matrix Z is searched. ij is 1, and the rest are 0;

[0045] Search for the inverse matrix F = DZ, F ij =1 indicates that there is an IEDj directly connected to IEDi in the reverse direction of the search of IED i. ji If it is 1, it means that there is an IEDi directly connected to IEDj in the reverse direction of IEDj's search; if the i-th row in the F matrix is ​​all zero, it means that there is no IED directly connected to IEDi in the reverse direction of IEDi's search.

[0046] Step 2-3) The revision of the network association description matrix D includes:

[0047] If the i-th row of F is 1, there is only one F ij =1, that is, in the reverse direction of IEDi’s search, only IEDi is directly connected to IEDi. ii , D ij Two elements, the rest remain unchanged, there is P ii =D ii +1=1,P ij =D ij -1=0;

[0048] If there is more than one 1 in the i-th row of F, F ij =1, F ik =1, that is, IEDj and IEDk are directly connected to IEDi in the reverse direction of IEDi search, and D in the revised matrix ii , D ij , D ik , the rest of the elements remain unchanged, and P ii =D ii +1=1,P ij =D ij -1=0,Pik =D ik -1=0;

[0049] If the i-th row of F is all zero, that is, there is no IED directly connected to i in the reverse direction of IEDi's search, then the elements of the i-th row in the matrix remain unchanged, that is, P ij =D ij .

[0050] Step 2-4) The fault search area can be located by the following criteria:

[0051] If P ij &P ji =1 (i≠j), the fault occurs between IEDi and IEDj, otherwise, there is no fault between them; its physical meaning is: IEDi and IEDj are adjacent, IEDj is in the search direction of IEDi, and IEDi is also in the search direction of IEDj, then the fault occurs between them;

[0052] If P ii =0, the node where this IED is located is an edge node, and the fault occurs upstream of the PV branch connected to this IED; its physical meaning is: if there is no IED directly connected to IEDi in the reverse direction of IEDi's search, then the node where this IED is located is an edge node, and the fault occurs upstream of the PV branch of this IED;

[0053] If P ii =1 and P ij = 0 (i≠j), that is, except for P in this row ii =1 and the other elements are all 0, then the node where this IED is located is an edge node, and the fault occurs downstream of the PV branch of this IED; its physical meaning is: in the reverse direction of IEDi's search, there is an IEDj directly connected to IEDi, and there is only one, then for the IED that processes three branches, the node where this IED is located is an edge node, and the fault occurs downstream of the PV branch of this IED.

[0054] The present invention has the following beneficial effects:

[0055] Compared with the prior art, the present invention proposes an improved algorithm for locating the fault area. The algorithm does not need to master the node information in advance. It collects and processes the current information through IED and determines the search direction to form the fault search positive direction matrix and the reverse direction matrix, and revises the network association description matrix according to the search reverse direction matrix. The algorithm does not distinguish between intermediate nodes and edge nodes, uses the same revision method, simplifies the algorithm, is adaptable to the changing network topology, and can clearly distinguish the two types of nodes in the criterion. There is no matrix multiplication operation, the amount of operation is small, and it has stability and versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a circuit diagram of a distribution network containing photovoltaic power sources under wide area protection of the present invention;

[0057] Figure 2 A flowchart of fault location of the present invention;

[0058] Figure 3 This is a three-branch circuit diagram of the present invention;

[0059] Figure 4 This is the positive sequence component sequence network diagram of the present invention;

[0060] Figure 5 This is a circuit diagram of a distribution network containing multiple PVs according to the present invention. DETAILED DESCRIPTION

[0061] The current wide area protection system is divided into two types: distributed decision-making and centralized decision-making. Distributed decision-making is to install an intelligent electronic device (IED) at each section switch. The IED is responsible for collecting and processing the electrical information of the installation point. Each IED exchanges information with the designated IED, and the fault is located by the set algorithm and then trips; centralized decision-making is to collect the information of all IEDs in the protection area by the host. There is no communication between IEDs. The host locates the fault section after analysis and judgment, and issues a tripping command to the corresponding IED. The present invention adopts a centralized decision-making structure based on the wide area protection system.

[0062] like Figure 1 As shown in Figure 1, there are two types of IEDs in the distribution network with photovoltaic power sources under wide area protection: IED A is used to sample and compare the comprehensive current amplitudes of three branches, and IED B is used to sample and compare the current phases of two branches. IED A has two types: intermediate nodes and edge nodes.

[0063] After a fault occurs, each IED A determines the fault area based on the comprehensive current amplitude of the three branches. If the fault occurs in the PV branch, the IED issues a trip command to the PV branch. If the PV branch has no fault, it communicates with the IED B in the determined fault area. Each IED B compares the phase relationship between the two branches and finally locates the fault section. The fault location process is as follows: Figure 2 The algorithm proposed in the present invention is only for the fault area location part.

[0064] The present invention proposes a method for locating a fault area in a photovoltaic power distribution network based on a wide area protection system, comprising the following steps:

[0065] Step 1) When a fault occurs, determine the search direction based on the fault area

[0066] 1-1) Determine the magnitude of the comprehensive current amplitude of the three-branch circuit:

[0067] The comprehensive current amplitude is the sum of the positive sequence component amplitude and the negative sequence component amplitude of the fault current, that is,

[0068]

[0069] Figure 3 It is a three-branch circuit. Figure 4 is the positive sequence component network diagram when a fault occurs. Assume that S a Impedance of the system

[0070] Z sa =|Z sa |∠α, impedance Z of DG1 ga =|Z ga |∠β, when fault occurs, the voltage of DG1 is U1=U1∠γ, ∠α and ∠β are impedance angles; ∠γ is the voltage phase of DG1, which is a parameter in the sinusoidal alternating current expression and is a known quantity that can be measured;

[0071] S a The positive sequence component of the system side branch is

[0072]

[0073] The positive sequence component of DG1 branch is

[0074]

[0075] The positive sequence component of the branch current pointing to the fault point is

[0076]

[0077] According to the cosine theorem, we can get

[0078]

[0079] Since the transient reactance of the generator is inductive, the impedance of the system and the line is also inductive, so α-β≈0, that is

[0080]

[0081]

[0082] The positive sequence current amplitude of the branch pointing to the fault point is the largest.

[0083] The same can be said

[0084]

[0085]

[0086] The negative sequence current amplitude of the branch pointing to the fault point is the largest.

[0087] In summary, the comprehensive amplitude of the current in the branch pointing to the fault point is the largest.

[0088] 1-2) According to the comparison result of the comprehensive current amplitude, determine the positive and reverse directions of the fault area search, specifically:

[0089] When a system fault occurs, the first step is to determine the size of the combined amplitude of the current in the three-branch circuit. The current direction of the branch with the largest amplitude is the positive direction of the fault area search. The current direction of the branch with the non-maximum amplitude is not the opposite direction of the fault search. The direction opposite to the positive search direction is the opposite direction of the fault area search.

[0090] Step 2) locate the fault area, including the following algorithms

[0091] 2-1) Construct a network association description matrix D to describe the neighbor relationship of the intelligent electronic devices IED at each segment switch.

[0092] A network association description matrix D is stored in the protection device to describe the neighbor relationship of each IED. The IEDs at the feeder nodes are numbered. Assuming there are n IEDs in total, an n×n square matrix D can be constructed, which is defined as follows:

[0093] If IEDi and IEDj are adjacent, then the corresponding element D in the network association description matrix D ij =1,D ji =1; if IED i and IED j are not adjacent, then the corresponding element D in the network association description matrix D ij =0,D ji =0; all D in the matrix ii =0, that is, all elements on the diagonal of the network association description matrix D are 0.

[0094] 2-2) The fault search direction is stored in the form of a matrix, the positive direction of the fault search is Z, and the fault search reverse direction matrix F=DZ is calculated.

[0095] Each IED samples and compares the comprehensive current amplitude of the three branches, determines the fault search direction, communicates with the centralized controller, and stores the fault search direction in the form of a matrix, with the positive fault search direction being Z and the negative fault search direction being F.

[0096] The current comprehensive amplitudes of the three branches of each IED A are compared one by one. For IEDi, if the fault search direction is determined to be the adjacent IEDj after comparing the current comprehensive amplitudes, the element Z in the jth column of the i-th row in the positive direction matrix Z is searched. ij is 1, and the rest of the elements are 0.

[0097] Search for the inverse matrix F = DZ, F ij=1 indicates that there is an IEDj directly connected to IEDi in the reverse direction of the search of IED i. ji If it is 1, it means that there is an IEDi directly connected to IEDj in the reverse direction of IEDj's search; if the i-th row in the F matrix is ​​all zero, it means that there is no IED directly connected to IEDi in the reverse direction of IEDi's search.

[0098] 2-3) Based on the search reverse matrix F, the network association description matrix D is revised, and the result of the revision is the fault discrimination matrix P.

[0099] When a fault occurs in the distribution network, each IED A samples and compares the comprehensive current amplitudes of the three branches to determine the direction of the fault search, and then revises the network association description matrix D according to the search reverse direction matrix. The result of the revision is the fault discrimination matrix P.

[0100] Revision of the network correlation description matrix D:

[0101] 1) If there is only one element F whose i-th row is 1 ij =1, that is, in the reverse direction of IEDi’s search, only IEDi is directly connected to IEDi. ii , D ij Two elements, the rest remain unchanged, there is P ii =D ii +1=1,P ij =D ij -1=0.

[0102] 2) If there is more than one 1 in the i-th row of F, F ij =1, F ik =1, that is, IEDj and IEDk are directly connected to IEDi in the reverse direction of IEDi search, and D in the revised matrix ii , D ij , D ik , the rest of the elements remain unchanged, and P ii =D ii +1=1,P ij =D ij -1=0,P ik =D ik -1=0.

[0103] 3) If the i-th row of F is all zero, that is, there is no IED directly connected to i in the reverse direction of IEDi's search, then the elements of the i-th row in the matrix remain unchanged, that is, P ij =D ij .

[0104] 2-4) Analyze the fault discrimination matrix P to identify the fault occurrence area:

[0105] The fault search area can be located by the following criteria:

[0106] 1) If P ij &P ji =1(i≠j), the fault occurs between IEDi and IEDj, otherwise, there is no fault between the two. Its physical meaning is: IEDi and IEDj are adjacent, IEDj is in the search direction of IEDi, and IEDi is also in the search direction of IEDj, then the fault occurs between the two.

[0107] 2) If P ii =0, the node where this IED is located is an edge node, and the fault occurs upstream of the PV branch connected to this IED. Its physical meaning is: if there is no IED directly connected to IEDi in the reverse direction of IEDi's search, then the node where this IED is located is an edge node, and the fault occurs upstream of the PV branch of this IED.

[0108] 3) If P ii =1 and P ij = 0 (i≠j), that is, except for P in this row ii =1 and the rest of the elements are 0, then the node where this IED is located is an edge node, and the fault occurs downstream of the PV branch of this IED. Its physical meaning is: there is an IEDj directly connected to IEDi in the reverse direction of IEDi's search, and there is only one. Then for the IED that processes three branches, the node where this IED is located is an edge node, and the fault occurs downstream of the PV branch of this IED.

[0109] Case Analysis

[0110] Figure 5 It is a typical distribution network with multiple photovoltaic power sources under wide area protection. The number of each node represents the number of each IEDA.

[0111] According to the connection status of each node, the network association description matrix D is formed as follows:

[0112]

[0113] 1. The fault occurs between intermediate nodes:

[0114] When a fault occurs at F1 upstream of PV4, the IED compares the comprehensive current amplitudes of the three branches, and the fault search positive direction matrix is:

[0115]

[0116] The fault search inverse matrix is

[0117]

[0118] The network association description matrix D is revised to obtain the fault discrimination matrix P:

[0119]

[0120] In P:P 12 &P 21 =0, the fault does not occur between IED 1 and IED 2, P 24 &P 42 =1, the fault occurs between IED 2 and IED 4, P 31 &P 13 =0, the fault does not occur between IED 1 and IED 3, P 44 =0, P 55 =0,P 66 =0, the node where IED 4, 5, and 6 are located is an edge node, and the fault occurs upstream of the PV branch of IED 4, 5, and 6. In summary, the fault occurs between IED 2 and IED 4.

[0121] 2. The fault occurs downstream of the edge node

[0122] A fault occurs at F2 downstream of PV4, and the fault search positive direction matrix is:

[0123]

[0124] The fault search inverse matrix is

[0125]

[0126] The fault discrimination matrix is ​​obtained as

[0127]

[0128] In the discriminant matrix P: P 12 &P 21 =0, the fault does not occur between IED 1 and IED 2, P 24 &P 42 =0, the fault does not occur between IED 2 and IED 4, P 31 &P 13 =0, the fault does not occur between IED 1 and IED 3, P 44 =1 and the rest of the elements are 0, then the node where IED 4 is located is an edge node, the fault occurs downstream of the PV branch of IED 4, P 55 =0,P 66 =0, the nodes where IED 5 and 6 are located are both edge nodes, and the fault occurs in the upstream of the PV branch of IED 5 and 6. In summary, the fault occurs in the downstream of the PV branch of IED 4.

Claims

1. A method for locating fault areas in a photovoltaic power distribution network based on a wide area protection system, characterized in that: The following steps are involved: 1) When a fault occurs, the search direction of the fault area is determined, including: 1-1) Determine the magnitude of the comprehensive current amplitude of the three-branch circuit; 1-2) According to the comparison result of the comprehensive current amplitude, determine the positive direction and reverse direction of the fault area search; 2) Locating the fault area includes the following algorithms: 2-1) Construct a network association description matrix D to describe the neighbor relationship of the intelligent electronic devices IED at each section switch; 2-2) The fault search direction is stored in the form of a matrix, the positive direction of the fault search is Z, and the fault search reverse direction matrix F=DZ is calculated; 2-3) The network association description matrix D is revised according to the search reverse direction matrix F, and the revised result is the fault discrimination matrix P; 2-4) Analyze the fault discrimination matrix P to identify the fault occurrence area; Wherein, step 2-1) constructing the network association description matrix includes: A network association description matrix D is stored in the protection device, and the IEDs at the feeder nodes are numbered. Assuming there are n IEDs in total, an n×n square matrix D can be constructed, which is defined as follows: If the i-th and j-th IEDs are adjacent, denoted as IEDi and IEDj, then the corresponding element D in the network association description matrix D is ij =1,D ji =1; if IEDi and IEDj are not adjacent, then the corresponding element D in the network association description matrix D ij =0,D ji =0; all D in the matrix ii =0, that is, all elements on the diagonal of the network association description matrix D are 0; Step 2-2) The calculation of the fault search reverse matrix includes: Each IED samples and compares the comprehensive current amplitude of the three branches, determines the fault search direction, communicates with the centralized controller, and stores the fault search direction in the form of a matrix, where the positive direction of the fault search is Z and the negative direction of the fault search is F. Among them, IED A is used to sample and compare the comprehensive current amplitude of the three branches; The current comprehensive amplitudes of the three branches of each IED A are compared one by one. For IEDi, if the fault search direction is determined to be the adjacent IEDj after comparing the current comprehensive amplitudes, then the element Z in the jth column of the i-th row in the positive direction matrix Z is searched. ij is 1, and the rest are 0; Search for the inverse matrix F = DZ, F ij =1 indicates that there is an IEDj directly connected to IEDi in the reverse direction of the search of IED i. ji If it is 1, it means that there is an IEDi directly connected to IEDj in the reverse direction of IEDj’s search; if the i-th row in the F matrix is ​​all zero, it means that there is no IED directly connected to IEDi in the reverse direction of IEDi’s search; Step 2-3) The revision of the network association description matrix D includes: If the i-th row of F is 1, there is only one F ij =1, that is, in the reverse direction of IEDi’s search, only IEDi is directly connected to IEDi. ii , D ij Two elements, the rest remain unchanged, there is P ii =D ii +1=1,P ij =D ij -1=0; If there is more than one 1 in the i-th row of F, F ij =1, F ik =1, that is, IEDj and IEDk are directly connected to IEDi in the reverse direction of IEDi search, and D in the revised matrix ii , D ij , D ik , the rest of the elements remain unchanged, and P ii =D ii +1=1,P ij =D ij -1=0,P ik =D ik -1=0; If the i-th row of F is all zero, that is, there is no IED directly connected to i in the reverse direction of IEDi's search, then the elements of the i-th row in the matrix remain unchanged, that is, P ij =D ij ; Step 2-4) The fault search area can be located by the following criteria: 1) If P ij &P ji =1 (i≠j), the fault occurs between IEDi and IEDj, otherwise, there is no fault between them; its physical meaning is: IEDi and IEDj are adjacent, IEDj is in the search direction of IEDi, and IEDi is also in the search direction of IEDj, then the fault occurs between them; 2) If P ii =0, the node where this IED is located is an edge node, and the fault occurs upstream of the PV branch connected to this IED; its physical meaning is: if there is no IED directly connected to IEDi in the reverse direction of IEDi's search, then the node where this IED is located is an edge node, and the fault occurs upstream of the PV branch of this IED; 3) If P ii =1 and P ij = 0 (i≠j), that is, except for P in this row ii =1 and the other elements are all 0, then the node where this IED is located is an edge node, and the fault occurs downstream of the PV branch of this IED; its physical meaning is: in the reverse direction of IEDi's search, there is an IEDj directly connected to IEDi, and there is only one, then for the IED that processes three branches, the node where this IED is located is an edge node, and the fault occurs downstream of the PV branch of this IED.

2. The method for locating a fault area in a photovoltaic power distribution network according to claim 1, characterized in that: Step 1-1) Comparison of the comprehensive amplitudes of the three-branch currents during a fault includes: The comprehensive current amplitude is the sum of the positive sequence component amplitude and the negative sequence component amplitude of the fault current, that is, Assume S a The impedance of the system is Z sa =|Z sa |∠α, impedance Z of DG1 ga =|Z ga |∠β, the voltage of DG1 during fault is U1=U1∠γ; ∠α and ∠β are impedance angles; ∠γ is the voltage phase of DG1, which is a parameter in the sinusoidal alternating current expression and is a measurable known quantity; S a The positive sequence component of the system side branch is The positive sequence component of DG1 branch is The positive sequence component of the branch current pointing to the fault point is According to the cosine theorem, we can get Since the transient reactance of the generator is inductive, the impedance of the system and the line is also inductive, so |α-β|≈0, that is, The positive sequence amplitude of the current in the branch pointing to the fault point is the largest; The same can be said The negative sequence amplitude of the current in the branch pointing to the fault point is the largest; then the comprehensive amplitude of the current in the branch pointing to the fault point is the largest.

3. The method for locating fault areas in a photovoltaic power distribution network according to claim 1, characterized in that: Step 1-2) specifically includes: based on the comparison of the comprehensive amplitudes of the currents in the three-branch circuits, the current direction of the branch with the largest amplitude is the positive direction of the fault area search, and the direction opposite to the positive search direction is the reverse direction of the fault area search.

Images