Fault phase selection method, device, equipment and medium based on LCL filter

Abstract

The present invention proposes a fault phase selection method, device, equipment and medium based on LCL filter, including constructing a single-phase grounding fault composite network model based on a distribution network structure with IIDG, the composite network model includes a first impedance unit, a second impedance unit and a third impedance unit connected in series in sequence, and the first impedance unit, the second impedance unit and the third impedance unit are all provided with LCL branches; obtaining the first mode current of the first impedance unit, the second mode current of the second impedance unit and the zero mode current of the third impedance unit; performing phase-mode conversion on the first mode current, the second mode current and the zero mode current to obtain the three-phase current of the LCL branch and perform phase conversion to obtain the branch current of the LCL branch; obtaining the current mutation amount of the branch current, performing fault phase selection according to the current mutation amount, and obtaining the fault phase of the distribution network structure. According to the technical solution of this embodiment, the fault phase selection can be conveniently and accurately performed through the significant response of the LCL branch to the transient component of the fault.

Description

Technical Field

[0001] The present invention relates to the technical field of power fault detection, and in particular to a fault phase selection method, device, equipment and medium based on an LCL filter. Background Art

[0002] At present, the distribution network mainly adopts the central point non-direct grounding operation mode. When a single-phase grounding fault occurs in the system, there may be an arc overvoltage problem at the fault point. In order to ensure reliable arc extinguishing, active intervention arc extinguishing devices are widely used. However, active intervention arc extinguishing devices can only inject compensation current into the distribution network to extinguish the arc under the premise of accurately identifying the fault phase. However, there are few research methods for phase selection of single-phase grounding faults in distribution networks. Most traditional phase selection methods use the amplitude and phase sequence of steady-state voltage for fault phase selection. However, when the power grid operates asymmetrically and the transition resistance is large, the traditional phase selection method will fail. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a fault phase selection method, device, equipment and medium based on LCL filter, which can quickly and accurately select the fault phase.

[0004] In a first aspect, an embodiment of the present invention provides a fault phase selection method based on an LCL filter, which is applied to a distribution network system, wherein the distribution network system includes a composite model, the composite model includes a first impedance unit, a second impedance unit, a third impedance unit and a transition resistor, one end of the first impedance unit is connected to one end of the transition resistor, the other end of the first impedance unit is connected to one end of the second impedance unit, the other end of the second impedance unit is connected to one end of the third impedance unit, and the other end of the third impedance unit is connected to the other end of the transition resistor, the first impedance unit is provided with an LCL branch, the LCL branch includes a first inductor and a first capacitor, the first inductor is connected to the first capacitor, the second impedance unit is the same as the first impedance unit, and the method includes:

[0005] Based on the distribution network structure with IIDG, a single-phase grounding fault composite network model is constructed, wherein the single-phase grounding fault composite network model comprises a first impedance unit, a second impedance unit and a third impedance unit connected in series in sequence, and the first impedance unit, the second impedance unit and the third impedance unit are all provided with an LCL branch;

[0006] Acquire a first-mode current of the first impedance unit, a second-mode current of the second impedance unit, and a zero-mode current of the third impedance unit;

[0007] Performing phase-mode conversion on the first-mode current, the second-mode current and the zero-mode current to obtain a three-phase current of the LCL branch;

[0008] Inverting the phase of the three-phase current to obtain the branch current of the LCL branch;

[0009] The current mutation amount of the branch current is obtained, and the fault phase is selected according to the current mutation amount to obtain the fault phase of the distribution network structure.

[0010] In some embodiments of the present invention, the performing phase-mode conversion on the first-mode current, the second-mode current and the zero-mode current further includes:

[0011] Acquire the second-mode current of the first impedance unit, the first-mode current of the second impedance unit, and the zero-mode current of the third impedance unit, as well as the main resonant component attenuation factor, the main resonant component amplitude, the main resonant frequency, and the main resonant component phase angle of the power distribution network system;

[0012] The first phase current, the second phase current and the third phase current are calculated according to the zero mode current, the first mode current, the second mode current, the main resonant component attenuation factor, the main resonant component amplitude, the main resonant frequency and the main resonant component phase angle.

[0013] In some embodiments of the present invention, the calculation of the first phase current, the second phase current and the third phase current is obtained according to the following formula:

[0014] ;

[0015] in, is the first phase current, is the second phase current, is the third phase current, is the first fault current, is the attenuation factor of the main resonant component; is the amplitude of the main resonant component; is the main resonant frequency; is the phase angle of the main resonant component.

[0016] In some embodiments of the present invention, before the phase shifting of the three-phase current, the method further includes:

[0017] Determine a transformer connection group between the LCL branch and the first fault point, and obtain a positive sequence current and a negative sequence current of the transformer, wherein the transformer connection group includes a first connection group and a second connection group;

[0018] When the transformer connection group is the first connection group, the positive sequence current on the Y side of the transformer leads the positive sequence current on the D side by 30 degrees, and the negative sequence current on the Y side of the transformer lags the negative sequence current on the D side by 30 degrees;

[0019] When the transformer connection group is the second connection group, the positive sequence current on the Y side of the transformer lags the positive sequence current on the D side by 30 degrees, and the negative sequence current on the D side of the transformer leads the negative sequence current on the D side by 30 degrees.

[0020] In some embodiments of the present invention, after obtaining the positive sequence current and the negative sequence current of the transformer, the method further comprises:

[0021] Obtaining three-phase current recording data of the LCL branch after a single-phase fault;

[0022] Calculate the first current mutation amount, the second current mutation amount and the third current mutation amount after the single-phase grounding fault according to the three-phase current recording data;

[0023] Performing wavelet transformation on the first current mutation amount, the second current mutation amount and the third current mutation amount to obtain a first high-frequency band energy, a second high-frequency band energy and a third high-frequency band energy;

[0024] A fault phase current is determined according to the first high-frequency band energy, the second high-frequency band energy, the third high-frequency band energy, the first connection group, and the second connection group.

[0025] In some embodiments of the present invention, the first impedance unit, the second impedance unit and the third impedance unit are all provided with a plurality of transformers, the distribution network structure is further provided with a first switch and a grounding transformer, one end of the first switch is grounded, the other end of the first switch is connected to one end of the grounding transformer, and the other end of the grounding transformer is respectively connected to the LCL branch and the plurality of transformers, and after the single-phase grounding fault composite network model is constructed, it also includes:

[0026] Determining an off state of the first switch, and determining an operation mode of a neutral point of the distribution network system according to the off state;

[0027] When the first switch is disconnected, the neutral point is not grounded;

[0028] When the first switch is closed, the neutral point is grounded through the arc suppression coil to determine the fault point of the single-phase grounding fault.

[0029] In some embodiments of the present invention, after determining the fault phase current according to the first high-frequency band energy, the second high-frequency band energy, the third high-frequency band energy, the first connection group and the second connection group, the method further includes:

[0030] When the connection group is the first connection group and the first grounded phase of the LCL branch is a single-phase grounding fault, the first high-frequency band energy and the third high-frequency band energy are much greater than the second high-frequency band energy;

[0031] When the second grounded phase of the LCL branch is a single-phase grounding fault, the first high-frequency band energy and the second high-frequency band energy are much greater than the third high-frequency band energy;

[0032] When the third grounded phase of the LCL branch is a single-phase grounding fault, the third high-frequency band energy and the second high-frequency band energy are much greater than the first high-frequency band energy;

[0033] When the connection group is the second connection group and the first grounded phase is a single-phase grounding fault, the first high-frequency band energy and the second high-frequency band energy are much greater than the third high-frequency band energy;

[0034] When the second grounded phase is a single-phase grounding fault, the second high-frequency band energy and the third high-frequency band energy are much greater than the first high-frequency band energy;

[0035] When the third grounded phase is a single-phase grounding fault, the third high-frequency band energy and the first high-frequency band energy are much greater than the second high-frequency band energy.

[0036] In a second aspect, an embodiment of the present invention provides a fault phase selection device based on an LCL filter, comprising at least one control processor and a memory for communicating with the at least one control processor; the memory stores instructions executable by the at least one control processor, and the instructions are executed by the at least one control processor so that the at least one control processor can execute the fault phase selection method based on the LCL filter as described in the first aspect above.

[0037] In a third aspect, an embodiment of the present invention provides an electronic device, comprising a fault phase selection device based on an LCL filter as described in the second aspect above.

[0038] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are used to execute the fault phase selection method based on the LCL filter as described in the first aspect above.

[0039] The fault phase selection method based on the LCL filter according to the embodiment of the present invention has at least the following beneficial effects:

[0040] Based on the distribution network structure with IIDG, a single-phase grounding fault composite network model is constructed, wherein the single-phase grounding fault composite network model includes a first impedance unit, a second impedance unit and a third impedance unit connected in series in sequence, and the first impedance unit, the second impedance unit and the third impedance unit are all provided with an LCL branch; the first mode current of the first impedance unit, the second mode current of the second impedance unit and the zero mode current of the third impedance unit are obtained; the first mode current, the second mode current and the zero mode current are phase-converted to obtain the three-phase current of the LCL branch; the three-phase current is phase-converted to obtain the branch current of the LCL branch; the current mutation amount of the branch current is obtained, and the fault phase is selected according to the current mutation amount to obtain the fault phase of the distribution network structure. According to the technical solution of this embodiment, the fault phase selection can be conveniently and accurately performed through the significant response of the LCL branch to the transient component of the fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a flow chart of a fault phase selection method based on an LCL filter provided by an embodiment of the present invention;

[0042] Figure 2 is a flow chart of performing phase-mode conversion on a first-mode current, a second-mode current and a zero-mode current according to an embodiment of the present invention;

[0043] Figure 3 This is a flow chart of an embodiment of the present invention before the three-phase current is phase-shifted;

[0044] Figure 4 is a flow chart after obtaining the positive sequence current and negative sequence current of the transformer according to an embodiment of the present invention;

[0045] Figure 5 is a flow chart after constructing a single-phase grounding fault composite network model according to an embodiment of the present invention;

[0046] Figure 6 It is a flow chart after determining the fault phase current according to the first high frequency band energy, the second high frequency band energy, the third high frequency band energy, the first connection group and the second connection group in an embodiment of the present invention;

[0047] Figure 7 is a schematic diagram of the principle of the distribution network structure of an embodiment of the present invention;

[0048] Figure 8 is a structural diagram of a composite network model according to an embodiment of the present invention;

[0049] Fig. 9 is a waveform diagram of the sudden change of three-phase current of the LCL capacitor branch after a fault in an embodiment of the present invention;

[0050] Fig.10is a waveform diagram of the square of high-frequency coefficients of each layer after wavelet transformation in an embodiment of the present invention;

[0051] Fig.11 is a schematic diagram of E6a under different fault positions and fault initial phase angles according to an embodiment of the present invention;

[0052] Fig.12 It is a structural diagram of a fault phase selection device based on an LCL filter provided in another embodiment of the present invention. DETAILED DESCRIPTION

[0053] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0054] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0055] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0056] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0057] Reference Figure 7The embodiment of the present invention provides a fault phase selection method based on an LCL filter, including constructing a single-phase grounding fault composite network model based on a distribution network structure with an IIDG, wherein the single-phase grounding fault composite network model includes a first impedance unit, a second impedance unit and a third impedance unit connected in series in sequence, and the first impedance unit, the second impedance unit and the third impedance unit are all provided with an LCL branch; obtaining a first-mode current of the first impedance unit, a second-mode current of the second impedance unit and a zero-mode current of the third impedance unit; performing phase-mode conversion on the first-mode current, the second-mode current and the zero-mode current to obtain a three-phase current of the LCL branch; performing phase conversion on the three-phase current to obtain a branch current of the LCL branch; obtaining a current mutation amount of the branch current, and performing fault phase selection according to the current mutation amount to obtain a fault phase of the distribution network structure. According to the technical solution of this embodiment, the capacitive reactance of the LCL branch is large for the power frequency component, and small for the transient high-frequency component of the fault. Due to the effect of the step-up transformer, the current response of the LCL branch is equivalent to a high-pass filtering of the transient current on the line and then amplification. Through the transient response characteristics of the three-phase current of the LCL capacitor branch during a single-phase grounding fault, there are obvious transient responses in two phases of the capacitor current mutation of the LCL branch, while the other phase is basically zero. Therefore, the significant response of the LCL branch to the transient component of the fault is used to conveniently and accurately select the fault phase.

[0058] The control method of the embodiment of the present invention is further described below based on the accompanying drawings.

[0059] Reference Figure 1 , Figure 1 A flow chart of a fault phase selection method based on an LCL filter provided in an embodiment of the present invention, the fault phase selection method based on the LCL filter includes but is not limited to the following steps:

[0060] Step S11, based on the distribution network structure with IIDG, construct a single-phase grounding fault composite network model, wherein the single-phase grounding fault composite network model includes a first impedance unit, a second impedance unit and a third impedance unit connected in series in sequence, and the first impedance unit, the second impedance unit and the third impedance unit are all provided with an LCL branch;

[0061] It should be noted that the transient process after a single-phase grounding fault occurs in the distribution network includes multiple resonance processes, and the resonance current is expressed by the following first formula:

[0062] ;

[0063] in, is the amplitude, is the angular frequency, is the initial phase angle, is the attenuation factor.

[0064] In the first formula, the frequency part with the largest amplitude is called the main resonant frequency, and the first resonant frequency is the main resonant frequency. When a single-phase grounding fault occurs, the transient resonant frequency is generally hundreds to thousands of Hz. Due to the existence of the LCL branch, the transient high-frequency signal in the distribution network structure is blocked by the LCL branch and will not flow through the inverter side. Therefore, Figure 7 The inverter side is equivalent to an open circuit for high-frequency components. Therefore, only the equivalent model of LCL in IIDG, that is, the system composite network model of the transient characteristic response of LCL capacitor current, needs to be considered.

[0065] Step S12, obtaining a first-mode current of the first impedance unit, a second-mode current of the second impedance unit, and a zero-mode current of the third impedance unit;

[0066] It should be noted that, refer to Figure 8 , L LCL is the line mode inductance of the LCL filter grid side; C LCL is the line mode capacitance of the LCL branch; Z1 is the impedance of the first impedance unit, that is, the line mode impedance of the system except the LCL branch; Z2 is the impedance of the second impedance unit, and the parameters of the second impedance unit are the same as those of the first impedance unit; Z0 is the zero mode impedance of the third impedance unit; R f is the fault transition resistance; i 1f 、i 2f 、i 0f are the first mode current, second mode current and zero mode current of the fault point respectively; i 1cf 、i 2cf are the first fault current and the second fault current of the LCL branch, i 0f is the third fault current.

[0067] From the boundary conditions of the single-phase ground short circuit fault, it can be seen that the first mode current, second mode current and zero mode current at the fault point are equal, which can be expressed by the following second formula:

[0068] ;

[0069] Since the network parameters of the second impedance unit are exactly the same as those of the first impedance unit, combined with the second formula, it can be obtained that the first-mode current and the second-mode current of the LCL branch are equal, that is, the third formula is obtained:

[0070] ;

[0071] Since the IIDG branch transformer T4 uses Δ / Y connection, there is no current zero-mode component on the secondary side (Y-shaped side) of the transformer. Let i0cf be the LCL branch zero-mode current, and the fourth formula is obtained:

[0072] =0.

[0073] Step S13, performing phase-mode conversion on the first-mode current, the second-mode current and the zero-mode current to obtain the three-phase current of the LCL branch;

[0074] Step S14, inverting the phase of the three-phase current to obtain the branch current of the LCL branch;

[0075] It should be noted that, since there is a Δ / Y connection transformer between the LCL filter and the fault point, there is a phase shift effect on the current. Further, according to the phase mode transformation, the first phase current i of the LCL capacitor branch can be obtained: acf , the second phase current i bcf and the third phase current i ccf , expressed by the fifth formula:

[0076] ;

[0077] Step S15, obtaining the current mutation amount of the branch current, and performing fault phase selection according to the current mutation amount to obtain the fault phase of the distribution network structure.

[0078] It should be noted that after a single-phase grounding fault occurs, among the first-phase current, the second-phase current and the third-phase current of the LCL branch, two phase currents have obvious transient mutations, while the phase current mutations of the remaining phases are basically zero. Fig. 9 As shown, the fault response characteristics are obvious, so accurate fault phase selection can be performed by detecting the current mutation amount of the LCL branch.

[0079] It should be noted that the capacitive reactance of the LCL branch is large for the power frequency component, but small for the transient high-frequency component of the fault. Due to the effect of the step-up transformer, the current response of the LCL branch is equivalent to a high-pass filtering of the transient current on the line and then amplification. Through the transient response characteristics of the three-phase current of the LCL capacitor branch during a single-phase grounding fault, there are obvious transient responses in two phases of the capacitor current mutation of the LCL branch, while the other phase is basically zero. Therefore, the significant response of the LCL branch to the transient component of the fault is used to conveniently and accurately select the fault phase.

[0080] In addition, in one embodiment, referring to Figure 2 ,exist Figure 1 Step S13 of the illustrated embodiment also includes but is not limited to the following steps:

[0081] Step S21, obtaining the second-mode current of the first impedance unit, the first-mode current of the second impedance unit, and the zero-mode current of the third impedance unit, as well as the main resonant component attenuation factor, the main resonant component amplitude, the main resonant frequency, and the main resonant component phase angle of the distribution network system;

[0082] Step S22, calculating the first phase current, the second phase current and the third phase current according to the zero mode current, the first mode current, the second mode current, the main resonant component attenuation factor, the main resonant component amplitude, the main resonant frequency and the main resonant component phase angle.

[0083] It should be noted that the fault transient current in the main resonance process includes the power frequency forced component and the main resonance free component, and the impedance of the LCL branch to the power frequency component is large. Therefore, the power frequency component response in the LCL branch is ignored, and the sixth formula is obtained:

[0084]

[0085] in, is the attenuation factor of the main resonant component; is the amplitude of the main resonant component; is the main resonant frequency; is the phase angle of the main resonant component.

[0086] Substituting the sixth formula into the fifth formula, we can further obtain the seventh formula:

[0087] ;

[0088] Among them, i acf is the first phase current, i bcf is the second phase current, i ccf is the third phase current, i 1cf is the first fault current, is the attenuation factor of the main resonant component; is the amplitude of the main resonant component; is the main resonant frequency; is the phase angle of the main resonant component.

[0089] In addition, in one embodiment, referring to Figure 3 ,exist Figure 1 Before step S14 of the illustrated embodiment, the following steps are also included but not limited to:

[0090] Step S31, determining a transformer connection group between the LCL branch and the first fault point, and obtaining a positive sequence current and a negative sequence current of the transformer, wherein the transformer connection group includes a first connection group and a second connection group;

[0091] Step S32, when the transformer connection group is the first connection group, the positive sequence current on the Y side of the transformer leads the positive sequence current on the D side by 30 degrees, and the negative sequence current on the Y side of the transformer lags the negative sequence current on the D side by 30 degrees;

[0092] Step S33, when the transformer connection group is the second connection group, the positive sequence current on the Y side of the transformer lags the positive sequence current on the D side by 30 degrees, and the negative sequence current on the D side of the transformer leads the negative sequence current on the D side by 30 degrees.

[0093] It should be noted that the transformer connection group includes a first connection group and a second connection group. In this embodiment, the first connection group is the Dy1 connection group, and the second connection group is the Dy11 connection group. When the transformer connection group is the second connection group (i.e., Dy11), the positive sequence current on the y side of the transformer leads the positive sequence current on the D side by 30 degrees, and the negative sequence current on the y side of the transformer lags the negative sequence current on the D side by 30 degrees, which can be expressed by the following eighth formula:

[0094] ;

[0095] Among them, I P ABC is the positive sequence component without phase shift, I N ABC is the negative sequence component before phase inversion, I P abc is the positive sequence component after phase shift, I N abc is the negative sequence component after phase shift.

[0096] Therefore, the current represented by the seventh formula needs to be inverted before it can be the actual current of the LCL branch. In this embodiment, the seventh formula is first written in the form of a phasor, and is expressed by the following ninth formula:

[0097] ;

[0098] Substituting the ninth formula into the eighth formula, we get the tenth formula:

[0099] ;

[0100] Then the current Iabc after phase rotation is expressed by the following eleventh formula:

[0101] = + = ;

[0102] It can be seen from the eleventh formula that when a single-phase grounding fault occurs in phase A of the LCL branch, and the transformer connection group is the second connection group (i.e., Dy11), the currents of phases A and C of the LCL branch will have transient responses, while the transient mutation of phase B current is basically zero. Similarly, it can be deduced that when a single-phase grounding fault occurs in phase B, only the capacitor currents of phases A and B will have transient mutations; when a single-phase grounding fault occurs in phase C, only the capacitor currents of phases B and C will have transient mutations.

[0103] When the transformer is in the first connection group (i.e. Dy1), the positive sequence current on the y side of the transformer lags behind the positive sequence current on the D side of the transformer by 30 degrees, and the negative sequence current on the y side of the transformer leads the negative sequence current on the D side of the transformer by 30 degrees. Similarly, when a single-phase grounding fault occurs on phase A, the capacitive currents of phases A and B of the LCL branch will experience a transient mutation, and the rest of the situations are similar.

[0104] In addition, in one embodiment, referring to Figure 4 ,exist Figure 3 After step S31 in the illustrated embodiment, the following steps are also included but not limited to:

[0105] Step S41, obtaining three-phase current recording data of the LCL branch after a single-phase fault;

[0106] Step S42, calculating the first current mutation amount, the second current mutation amount and the third current mutation amount after the single-phase grounding fault according to the three-phase current recording data;

[0107] Step S43, performing wavelet transformation on the first current mutation amount, the second current mutation amount and the third current mutation amount to obtain a first high frequency band energy, a second high frequency band energy and a third high frequency band energy;

[0108] Step S44, determining the fault phase current according to the first high frequency band energy, the second high frequency band energy, the third high frequency band energy, the first connection group and the second connection group.

[0109] It should be noted that the first current mutation of the LCL branch is The second current mutation is The third current mutation is , when the time window in the distribution network structure is preset to 20ms and the sampling frequency is preset to 10kHz, the twelfth formula is obtained:

[0110] ;

[0111] Where n is the number of sampling points.

[0112] In order to further improve the accuracy of fault phase identification, this embodiment uses wavelet transform to extract fault features from the current mutation. It can be understood by those skilled in the art that wavelet transform has good localization properties in the time-frequency domain and has the characteristics of multi-resolution analysis. Discrete wavelet transform is usually used in engineering applications. For the discrete signal samples of this embodiment, it can be expressed by the following thirteenth formula:

[0113]

[0114] ;

[0115] in, and are the approximation coefficient and detail coefficient of the jth layer respectively. and They are low pass filter and high pass filter respectively.

[0116] Furthermore, the high frequency band energy of the j-th layer signal is expressed by the following fourteenth formula:

[0117] 2 ;

[0118] It should be noted that when detecting high-order singular points of transient signals in power systems, it is necessary to select a wavelet basis with a certain order vanishing moment and a high center frequency. Since the db4 wavelet has a fourth-order vanishing moment and a high center frequency, this embodiment uses the db4 wavelet as the wavelet basis. Based on a sampling frequency of 10kHz, the A-phase current mutation is decomposed into seven layers, such as Fig.10 As shown (fault occurred at 0.382s), where d1 2 is the square of the high frequency coefficient of the first layer, d2 2 is the square of the second-layer high-frequency coefficient, and so on. The energy of each high-frequency band of the sudden change of the ABC three-phase current within 2ms after the fault occurs is calculated by the fourteenth formula as shown in Table 1 (A phase grounding fault, transformer T2 connection group is the first connection group). It can be seen from Table 1 that after the fault occurs, the energy of the sixth high-frequency band is the largest. It can be seen from this that in the embodiment Figure 7 The transient high-frequency energy after the distribution network structure fault is shown to be mainly concentrated in the frequency band of 156.25 Hz to 312.5 Hz, that is, the frequency band where the main resonant frequency is located. Therefore, the embodiment selects the high-frequency band energy of the sixth layer as the basis.

[0119] Table 1

[0120]

[0121] It should be noted that for different distribution network structures, structural topology and line parameters may cause the main resonant frequency to change, and it is necessary to reselect the layer number where the maximum high-frequency band energy is located.

[0122] In addition, in one embodiment, referring to Figure 5 ,exist Figure 1 After step S11 of the illustrated embodiment, the following steps are also included but not limited to:

[0123] Step S51, determining the off state of the first switch, and determining the operation mode of the neutral point of the distribution network system according to the off state;

[0124] Step S52, when the first switch is disconnected, the neutral point is not grounded;

[0125] Step S53: when the first switch is closed, the neutral point is grounded through the arc suppression coil to determine the fault point of the single-phase grounding fault.

[0126] It should be noted that the distribution network structure with IIDG is as follows Figure 7 As shown in the figure, the 35kV / 10kV step-down transformer T1 adopts Y / Δ connection, the 0.4kV / 10kV step-up transformer T2 adopts Y / Δ connection, the 10kV / 0.4kV distribution transformers T4, T5, T6, T7, and T8 adopt Δ / Y connection, and the grounding transformer T3 provides different neutral point modes for the 10kV side of the system triangle connection. When the first switch K is disconnected, and the distribution network structure operates in a neutral point ungrounded mode, when the first switch K is closed, the distribution network structure operates in a neutral point grounded mode through an arc suppression coil, then the fault point when a single-phase grounding fault occurs can be determined.

[0127] In addition, in one embodiment, referring to Figure 6 ,exist Figure 4 After step S44 in the illustrated embodiment, the following steps are also included but not limited to:

[0128] Step S61, when the connection group is the first connection group and the first grounded phase of the LCL branch is a single-phase grounding fault, the first high frequency band energy and the third high frequency band energy are much greater than the second high frequency band energy;

[0129] Step S62, when the second grounded phase of the LCL branch is a single-phase grounding fault, the first high-frequency band energy and the second high-frequency band energy are much greater than the third high-frequency band energy;

[0130] Step S63, when the third grounded phase of the LCL branch is a single-phase grounding fault, the third high-frequency band energy and the second high-frequency band energy are much greater than the first high-frequency band energy;

[0131] Step S64, when the connection group is the second connection group and the first grounded phase is a single-phase grounding fault, the first high-frequency band energy and the second high-frequency band energy are much greater than the third high-frequency band energy;

[0132] Step S65, when the second grounded phase is a single-phase grounding fault, the second high-frequency band energy and the third high-frequency band energy are much greater than the first high-frequency band energy;

[0133] Step S66: When the third grounded phase is a single-phase grounding fault, the third high-frequency band energy and the first high-frequency band energy are much greater than the second high-frequency band energy.

[0134] It should be noted that, from the eleventh formula, after a single-phase grounding fault occurs, the current mutations of the two phases of the LCL branch are basically equal, and the current mutation of the remaining phase is basically zero. Therefore, the high-frequency energy E6 obtained after wavelet transform has two phases that are basically equal and much larger than the other phase. Therefore, when the LCL branch transformer connection group is the second connection group (Dy11), the phase selection criterion can be expressed by the fifteenth formula:

[0135] ;

[0136] When the transformer connection group is the first connection group (Dy1), it is expressed by the sixteenth formula:

[0137] ;

[0138] After a fault occurs, the zero-sequence current mutation is detected to start the phase selection algorithm, and the first current mutation 2ms after the fault is calculated through the LCL branch three-phase current recording data. , the second current mutation and the third current mutation , then the first current mutation amount, the second current mutation amount and the third current mutation amount are subjected to wavelet transform, and the first high-frequency band energy E6a, the second high-frequency band energy E6b and the third high-frequency band energy E6c of the sixth layer are calculated. After considering the actual operation connection group of the transformer, the fault phase is determined according to the fifteenth formula and the sixteenth formula.

[0139] The specific simulation process of this embodiment is as follows:

[0140] Based on matlab / simulink Figure 8 The single-phase ground fault network model of the distribution network structure shown in the figure. The feeder parameters are as follows: positive sequence resistance is 0.27Ω / km, zero sequence resistance is 0.42Ω / km; positive sequence inductance is 1.1mH / km, zero sequence inductance is 11.5mH / km; positive sequence capacitance is 10.116nF / km, zero sequence capacitance is 21.522nF / km. The grid-connected capacity of the inverter system is 500kW, the rated capacity of the main transformer T1 is SN1=10MVA, the impedance voltage percentage is Uk1%=10.5; the rated capacity of transformer T2 is SN2=630kVA, the impedance voltage percentage is Uk2%=3, and the connection group is Dy1; the rated capacities of distribution transformers T4~T8 are SN4=250kVA, SN5=200kVA, SN6=100kVA, SN7=100kVA, SN8=100kVA, and the impedance voltage percentage is Uk4~8%=3. The load of each distribution transformer is set to 90% of the rated capacity and the power factor is 0.9. The system frequency is 50Hz and the sampling frequency of the LCL branch capacitor current is 10kHz. The fault point F is located on the first outgoing line.

[0141] The parameters of the LCL branch are as follows: inverter side inductor L1 = 0.24mH, grid side inductor L2 = 0.08mH, filter capacitor C1 = 220uF. In order to suppress the LCL resonance spike, active damping or passive damping solutions are usually used to increase the system damping. The passive damping solution directly connects the actual resistance in series with the filter capacitor branch, while the active damping solution suppresses the resonance spike by designing a control strategy without introducing an actual resistance. If the passive damping solution is adopted, the damping resistor on the filter capacitor branch side increases the branch impedance, which will reduce the amplitude of the transient high-frequency component; if the active damping solution is adopted, there will be no effect. In the simulation of this article, the passive damping solution is adopted, and the damping resistor is RLCL = 0.17Ω.

[0142] Phase selection results and analysis under the neutral point ungrounded mode:

[0143] Assume that the distribution network structure operates in a neutral point ungrounded mode, and a phase A grounding fault occurs at the fault point. The fault point is located at a distance of 8 km from the busbar on line 1. The initial phase angle of the fault is 10°. The transition resistance is set to 10Ω, 1000Ω, 2000Ω, 3000Ω, and 4000Ω. The sixth layer high frequency band energy E6a, E6b, and E6c of the current mutation amount 2ms after the fault are shown in Table 2. It can be seen from Table 2 that the phase selection result proposed in this embodiment is correct and reliable when the transition resistance is low; when the transition resistance reaches 4000Ω, although E6a and E6c are reduced, they still meet Relationship, it still has good applicability under high resistance grounding conditions.

[0144] Table 2

[0145]

[0146] The influence of different fault locations and initial fault phase angles:

[0147] Changing the position of the fault point on line 1 and the initial phase angle of the fault, the transition resistance is 3000Ω, and the other conditions remain unchanged. The change of the sixth layer high frequency band energy E6a of the current mutation 2ms after the fault is as follows: Fig.11 As shown. It can be seen that E6a has a maximum value when the initial fault phase angle is 90°, and a minimum value when the initial fault phase angle is 0°, and decreases with the increase of the distance from the fault point to the busbar. Under the extreme condition that the initial fault phase angle is 0° and the fault point is located at the end of line 1 18km away from the busbar, E6a, E6b, and E6c are 11.21, 11.03, and 0.031 respectively, and there is still , the phase can be selected correctly. Since the fault occurs when the initial phase angle is 0°, the fault phase voltage is 0, and the fault phase-to-ground capacitance discharge current is very small, but the non-fault phase charging current related to the line mode component still exists, so the phase selection strategy of this embodiment is still applicable.

[0148] Phase selection results when the neutral point is grounded through an arc suppression coil:

[0149] Since the main resonant frequency is much larger than the power frequency, under the main resonant frequency condition, the arc suppression coil inductance reactance is much larger than the system ground distributed capacitance reactance, so the arc suppression coil has almost no effect on the high-frequency component. The system neutral point is assumed to be grounded through the arc suppression coil, the overcompensation coefficient is 1.05, and the other conditions are the same as the above conditions. The sixth layer of high-frequency band energy E6a, E6b, and E6c of the current mutation 2ms after the fault are shown in Table 3. By comparing Table 3 with Table 2, it can be seen that under the same transition resistance fault condition, the E6a, E6b, and E6c of the neutral point grounded system through the arc suppression coil have almost no change compared with the neutral point ungrounded system, which is consistent with the conclusion of the analysis and can correctly select the phase.

[0150] Table 3

[0151]

[0152] Phase selection results under asymmetric grid conditions:

[0153] Grid asymmetry is generally manifested as unbalanced system-to-ground distributed parameters, that is, the three-phase resistance and capacitance values ​​to ground are different. The zero-mode component representing the ground loop will be affected, but the line-mode component is almost unaffected. Considering that there is no zero-mode component of current on the secondary side (Y-shaped side) of the transformer, the above conclusion is still applicable.

[0154] In general, the asymmetry of the power grid line is usually 0.5%~1.5%, and the theoretical limit is 3.5%. Assuming that the distribution network structure operates under the condition of neutral point grounding through arc suppression coil, the overcompensation coefficient is 1.05, and the power grid asymmetry is set to 2.44%, and the other conditions are the same as the above conditions. The sixth layer high frequency band energy E6a, E6b, and E6c of the current mutation 2ms after the fault are shown in Table 4. It can be seen from Table 4 that the phase can still be selected correctly under asymmetric operating conditions.

[0155] Table 4

[0156]

[0157] Table 4

[0158] like Fig.12 As shown, Fig.12 : is a structural diagram of a fault phase selection device based on an LCL filter provided by an embodiment of the present invention. The present invention also provides a fault phase selection device based on an LCL filter, comprising:

[0159] The processor 1201 may be implemented by a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of the present application;

[0160] The memory 1202 can be implemented in the form of a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 1202 can store an operating system and other application programs. When the technical solution provided in the embodiment of this specification is implemented by software or firmware, the relevant program code is stored in the memory 1202, and the processor 1201 calls and executes the fault phase selection method based on the LCL filter in the embodiment of the present application;

[0161] Input / output interface 1203, used to implement information input and output;

[0162] The communication interface 1204 is used to realize the communication interaction between the apparatus and other devices. The communication can be realized through a wired manner (such as USB, network cable, etc.) or a wireless manner (such as mobile network, WIFI, Bluetooth, etc.);

[0163] A bus 1205 that transmits information between various components of the device (e.g., the processor 1201, the memory 1202, the input / output interface 1203, and the communication interface 1204);

[0164] The processor 1201 , the memory 1202 , the input / output interface 1203 and the communication interface 1204 are connected to each other in communication within the device via the bus 1205 .

[0165] An embodiment of the present application also provides an electronic device, comprising the fault phase selection device based on the LCL filter as described above.

[0166] An embodiment of the present application further provides a storage medium, which is a computer-readable storage medium and stores a computer program. When the computer program is executed by a processor, the above-mentioned fault phase selection method based on the LCL filter is implemented.

[0167] As a non-transient computer-readable storage medium, the memory can be used to store non-transient software programs and non-transient computer executable programs. In addition, the memory may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage devices. In some embodiments, the memory may optionally include a memory remotely arranged relative to the processor, and these remote memories may be connected to the processor via a network. Examples of the above-mentioned networks include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof. The device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and are implemented to be located in one place, or may also be distributed to multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment.

[0168] It will be appreciated by those skilled in the art that all or some of the steps and systems in the methods disclosed above may be implemented as software, firmware, hardware, and appropriate combinations thereof. Some or all physical components may be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit. Such software may be distributed on a computer-readable medium, which may include a computer storage medium (or non-transitory medium) and a communication medium (or transient medium). As known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, it is well known to those skilled in the art that communication media generally include computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0169] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the above-mentioned implementation mode. Technical personnel familiar with the field can also make various equivalent deformations or substitutions under the shared conditions without violating the spirit of the present invention. These equivalent deformations or substitutions are all included in the scope defined by the claims of the present invention.

Claims

1. A fault phase selection method based on LCL filter, characterized in that: Applied in a distribution network system, the distribution network system includes a composite model, the composite model includes a first impedance unit, a second impedance unit, a third impedance unit and a transition resistor, one end of the first impedance unit is connected to one end of the transition resistor, the other end of the first impedance unit is connected to one end of the second impedance unit, the other end of the second impedance unit is connected to one end of the third impedance unit, the other end of the third impedance unit is connected to the other end of the transition resistor, the first impedance unit, the second impedance unit and the third impedance unit are all provided with an LCL branch, the LCL branch includes a first inductor and a first capacitor, the first inductor is connected to the first capacitor, the second impedance unit is the same as the first impedance unit, and the method includes: Obtaining a first fault point of the first impedance unit, a second fault point of the second impedance unit, and a third fault point of the third impedance unit, and obtaining a first fault current of the first fault point, a second fault current of the second fault point, and a third fault current of the third fault point; Performing linear transformation on the first fault current, the second fault current and the third fault current to obtain a first phase current, a second phase current and a third phase current of the LCL branch; Performing phase shifting on the first phase current, the second phase current and the third phase current to obtain a branch current of the LCL branch; The fault current mutation amount of the LCL branch is obtained, and the fault phase is selected according to the current mutation amount to obtain the fault phase of the distribution network system.

2. The fault phase selection method based on LCL filter according to claim 1, characterized in that: After the first fault current, the second fault current and the third fault current are linearly transformed, the method further includes: Acquire the second-mode current of the first impedance unit, the first-mode current of the second impedance unit, and the zero-mode current of the third impedance unit, as well as the main resonant component attenuation factor, the main resonant component amplitude, the main resonant frequency, and the main resonant component phase angle of the power distribution network system; The first phase current, the second phase current and the third phase current are calculated according to the zero mode current, the first mode current, the second mode current, the main resonant component attenuation factor, the main resonant component amplitude, the main resonant frequency and the main resonant component phase angle.

3. The fault phase selection method based on LCL filter according to claim 2 is characterized in that: The first phase current, the second phase current and the third phase current are calculated according to the following formula: ； in, is the first phase current, is the second phase current, is the third phase current, is the first fault current, is the attenuation factor of the main resonant component; is the amplitude of the main resonant component; is the main resonant frequency; is the phase angle of the main resonant component.

4. The fault phase selection method based on LCL filter according to claim 1, characterized in that: A transformer is provided between the LCL branch and the first fault point. Before the phase conversion of the first phase current, the second phase current and the third phase current is performed, the method further includes: Determine a transformer connection group between the LCL branch and the first fault point, and obtain a positive sequence current and a negative sequence current of the transformer, wherein the transformer connection group includes a first connection group and a second connection group; When the transformer connection group is the first connection group, the positive sequence current on the Y side of the transformer leads the positive sequence current on the D side by 30 degrees, and the negative sequence current on the Y side of the transformer lags the negative sequence current on the D side by 30 degrees; When the transformer connection group is the second connection group, the positive sequence current on the Y side of the transformer lags the positive sequence current on the D side by 30 degrees, and the negative sequence current on the D side of the transformer leads the negative sequence current on the D side by 30 degrees.

5. The fault phase selection method based on LCL filter according to claim 4 is characterized in that: After the positive sequence current and negative sequence current of the transformer are obtained, the method further comprises: Obtaining three-phase current recording data of the LCL branch after a single-phase fault; Calculate the first current mutation amount, the second current mutation amount and the third current mutation amount after the fault according to the three-phase current recording data; Performing wavelet transformation on the first current mutation amount, the second current mutation amount and the third current mutation amount to obtain a first high-frequency band energy, a second high-frequency band energy and a third high-frequency band energy; A fault phase current is determined according to the first high-frequency band energy, the second high-frequency band energy, the third high-frequency band energy, the first connection group, and the second connection group.

6. The fault phase selection method based on LCL filter according to claim 1, characterized in that: The first impedance unit, the second impedance unit and the third impedance unit are all provided with a plurality of transformers, the distribution network system is further provided with a first switch and a grounding transformer, one end of the first switch is grounded, the other end of the first switch is connected to one end of the grounding transformer, and the other end of the grounding transformer is respectively connected to the LCL branch and the plurality of transformers, and before obtaining the first fault point of the first impedance unit, it also includes: Determining an off state of the first switch, and determining an operation mode of a neutral point of the distribution network system according to the off state; When the first switch is disconnected, the neutral point is not grounded; When the first switch is closed, the neutral point is grounded through the arc suppression coil to determine the fault point of the single-phase grounding fault.

7. A fault phase selection device based on LCL filter, characterized in that: It includes at least one control processor and a memory for communicating with the at least one control processor; the memory stores instructions that can be executed by the at least one control processor, and the instructions are executed by the at least one control processor so that the at least one control processor can execute the fault phase selection method based on the LCL filter as described in any one of claims 1 to 6.

8. An electronic device, characterized in that: It includes the fault phase selection device based on LCL filter as described in claim 7.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the fault phase selection method based on the LCL filter as described in any one of claims 1 to 6.

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