A method, device and medium for calculating laminar flow distribution of multi-layer superconducting cable

Abstract

The present invention relates to a method, device and medium for calculating laminar flow distribution of a multi-layer superconducting cable, wherein the method comprises the following steps: constructing an equivalent circuit diagram of a multi-layer superconducting cable; according to the equivalent circuit diagram, writing the Kirchhoff voltage equations of each phase and each layer for each order current component and combining them into a matrix form; according to the Kirchhoff voltage equation matrix, solving the voltage magnitude of each phase by using the current magnitude of each phase and the current relationship between the conductive layer and the shielding layer; solving the current distribution of each layer by using the same voltage of each layer in each phase. Compared with the prior art, the present invention can directly use the parameters of each order from the power grid current as the data source to solve the current distribution between the layers of the harmonic component, thereby more accurately reflecting the distribution of the harmonic current of each layer and the influence on the AC loss characteristics of the superconducting cable.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission and distribution, and in particular to a method, device and medium for calculating laminar flow distribution of a multilayer superconducting cable taking into account the influence of harmonic current. Background Art

[0002] Superconducting cables have great development potential as a transmission medium due to their significant advantages such as large transmission capacity, high transmission efficiency, and small pipeline body volume. In new power systems, due to the addition of more and more power electronic devices and nonlinear loads, the emergence of harmonic currents in the system is inevitable. When the current containing harmonic components is transmitted through superconducting cables, the superconducting cables will generate more AC losses in the form of heat. Therefore, in order to ensure the low-loss characteristics of superconducting cables, the influence of harmonic currents is fully considered, and the laminar flow distribution of the load current of superconducting cables containing harmonic components is accurately solved, which plays an important role in the subsequent calculation of AC losses. In the existing research on the solution of AC losses when superconducting cables contain harmonic components, the research object is mostly assumed to be a single-layer structure (that is, each of the three phases contains a layer of superconducting tape). During the calculation, the harmonic current with the set amplitude, order, phase and other parameters is directly applied to the symmetrical three-phase current. The influence of harmonic current on superconducting cables is studied by solving the AC loss of this current. Compared with single-layer superconducting cables, multi-layer superconducting cables (three phases each containing two or more layers of superconducting tapes) can increase the current transmission capability by stacking multiple superconducting layers in the same cable, providing a larger current capacity. However, due to the different winding structures of each layer, current shunting will occur. At this time, if the harmonic current is directly applied to the original shunting of each layer for research, it cannot represent the total current size after each layer is actually shunted. Therefore, there is currently a lack of a calculation method that can accurately calculate the current size of each layer. Summary of the invention

[0003] The purpose of the present invention is to provide a method, device and medium for calculating the laminar flow distribution of a multi-layer superconducting cable taking into account the influence of harmonic currents, taking into account the influence of harmonic currents on the current distribution of each layer in a multi-layer superconducting tape, using the current parameters of each order obtained by digital signal processing of the actual load current waveform of the power grid as a data source, and quantitatively calculating the current distribution of each layer of the multi-layer superconducting cable due to the influence of harmonic currents, thereby more accurately reflecting the influence of harmonic currents on the AC loss characteristics of the superconducting cable.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A method for calculating laminar flow distribution of a multilayer superconducting cable considering the influence of harmonic currents comprises the following steps:

[0006] Step 1) constructing a multilayer superconducting cable equivalent circuit diagram;

[0007] Step 2) According to the equivalent circuit diagram, write the Kirchhoff voltage equations for each phase and each layer for each order current containing harmonic components and combine them into a matrix form;

[0008] Step 3) According to the Kirchhoff voltage equation matrix, the voltage magnitude of each phase is solved by using the current magnitude of each phase and the current relationship between the conductive layer and the shielding layer;

[0009] Step 4) Using the same voltage across layers in each phase, solve for the current distribution in each layer.

[0010] Assume that each phase of a multi-layer superconducting cable has n conductive layers and n shielding layers. According to the equivalent circuit diagram, the current of each phase in the multi-layer superconducting cable is divided into n layers. The relationship between the current of each phase and its layer current is:

[0011] I A =I A1 +I A2 +…I An

[0012] I B =I B1 +I B2 +…I Bn

[0013] I C =I C1 +I C2 +…I Cn

[0014] I S =I S1 +I S2 +…I Sn

[0015] Among them, I A ,I B ,I C Respectively represent the current of the conductive layer phase A, phase B, and phase C, I S Represents the shield current, I Ai ,I Bi ,I Ci ,I Si They represent the currents of the conductive layer phase A, phase B, phase C and the i-th layer of the shielding layer respectively.

[0016] In the step 2), the equivalent resistance part of the cable body is ignored when writing the Kirchhoff voltage equation for each phase and each layer.

[0017] The Kirchhoff voltage equation matrix is ​​expressed as:

[0018]

[0019] Among them, A and B represent the inverse matrix of the inductance matrix and the capacitance matrix respectively, I Ai ,I Bi ,I Ci ,I Si They represent the currents of the conductive layer phase A, phase B, phase C and the shielding layer i, respectively, U Ai , U Bi , U Ci , U Si They represent the voltages of the conductive layer phase A, phase B, phase C and the i-th layer of the shielding layer respectively.

[0020] Set the current in the shield layer to the inverse of the sum of the three-phase harmonic currents, and determine the voltage relationship based on the parallel relationship between the conductive layers in each phase:

[0021] U A1 =U A2 =…U An

[0022] U B1 =U B2 =…U Bn

[0023] U C1 =U C2 =…U Cn

[0024] U S1 =U S2 =…U Sn

[0025] The step 3) comprises the following steps:

[0026] Step 3-1) Assume that the highest order of harmonic components is m, and consider the three-phase AC current I when the power grid contains harmonic components A ,I B ,I C It is expressed as:

[0027]

[0028]

[0029]

[0030] Among them, I k They represent the kth harmonic amplitude of the three-phase current, θ k They represent the kth harmonic phase angle of the three-phase current respectively;

[0031] Step 3-2) According to the voltage relationship and the relationship between each phase current and its layer current, add the n-layer Kirchhoff voltage equations of each phase in the Kirchhoff voltage equation matrix to obtain:

[0032]

[0033] Among them, C ab , C bc , C cs Respectively represent the capacitance between AB phases, between BC phases, between C phase and shielding layer, M ab represents the sum of the inductance values ​​within the cross-coverage range of n layers and n rows belonging to subscript a and n layers and n columns belonging to subscript b in matrix A. Subscript 1 represents phase A, subscript 2 represents phase B, subscript 3 represents phase C, and subscript 4 represents the shielding layer, that is, M 11 represents the sum of the inductance values ​​within the cross coverage of n rows and n columns belonging to n layers of phase A in matrix A, M 12 represents the sum of the inductance values ​​within the cross-coverage range of n rows belonging to n layers of phase A and n columns belonging to n layers of phase B in matrix A, M 21 represents the sum of the inductance values ​​within the cross-coverage range of n rows belonging to n layers of phase B and n columns belonging to n layers of phase A in matrix A, and so on;

[0034] Step 3-3) Take two conductive layers and one shielding layer per phase as the research structure, and transform the inverse matrix of the inductance matrix Denoted as A', the capacitance matrix Denoted as B', considering the three-phase current contains harmonic components of different orders: ω, 3ω, 5ω, 7ω...mω, use the following formula to calculate the 1st, 3rd...mth voltage:

[0035]

[0036] Among them, I Am ,I Bm ,I Cm Respectively represent the m-order harmonic current amplitude in phase A, phase B, and phase C current, U Am , U Bm , U Cm They represent the voltages generated in the circuit by the m-order harmonic currents in the A-phase, B-phase, and C-phase currents respectively. Represents the magnitude of the shielding layer current in the case of m-order harmonic current, that is, the negative number of the sum of the conductive layer currents.

[0037] In step 4), the harmonic currents of each order in each layer are solved according to the following formula:

[0038]

[0039] Among them, I A1m ,I B1m ,I C1mThey represent the current distribution of the m-order harmonic current in the first superconducting layer of the superconducting cable phase A, phase B, and phase C, respectively. A2m ,I B2m ,I C2m They represent the current distribution of the m-order harmonic current in the second superconducting layer of phase A, phase B, and phase C of the superconducting cable, respectively. Sm It represents the current distribution of m-order harmonic current in the shielding layer of superconducting cable.

[0040] In step 4), the harmonic currents of each layer are superimposed to obtain the total current distribution of each layer:

[0041]

[0042]

[0043]

[0044]

[0045] A device for calculating laminar flow distribution of a multilayer superconducting cable taking into account the influence of harmonic currents comprises a memory, a processor, and a program stored in the memory. When the processor executes the program, the method described above is implemented.

[0046] A storage medium stores a program, which implements the method described above when executed.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention fully considers the characteristics of the complex frequency domain changing with the harmonic current frequency in the calculation of the inductance and capacitance in the superconducting cable equivalent circuit model, and also considers the differences in the winding structures of each layer in the multi-layer superconducting cable, which leads to different distributions of harmonic components between different layers. The proposed quantitative calculation method for the interlayer current distribution when considering the influence of the harmonic current components has a simple and clear calculation principle and is easy to operate. It can directly use the various order parameters from the power grid current as the data source to solve the interlayer current distribution of the harmonic component, thereby more accurately reflecting the distribution of the harmonic current in each layer and the influence on the AC loss characteristics of the superconducting cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a flow chart of the method of the present invention;

[0050] Figure 2 1 is an equivalent circuit diagram of a three-phase coaxial multilayer superconducting cable in an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0052] Example 1

[0053] This embodiment provides a method for calculating laminar flow distribution of a multilayer superconducting cable taking into account the influence of harmonic currents. Figure 1 As shown, the following steps are included:

[0054] Step 1) Construct a multilayer superconducting cable equivalent circuit diagram.

[0055] Figure 2 This is the equivalent circuit diagram of a three-phase coaxial multilayer superconducting cable. Assume that there are n conducting layers and n shielding layers in each phase. Figure 2 In the equivalent circuit diagram, R A1 , R A2 ……R Sn , L A1 , L A2 ...L Sn Respectively represent the resistance and inductance of each layer in each phase including the shielding layer, C ab , C bc , C cs Represents the capacitance between each phase, I A ,I B ,I C Respectively represent the current of the conductive layer phase A, phase B, and phase C, I S Indicates the shield current.

[0056] Step 2) According to the equivalent circuit diagram, write the Kirchhoff voltage equations for each phase and each layer for each order current containing harmonic components and combine them into a matrix form.

[0057] according to Figure 2 The Kirchhoff voltage equation for each phase and layer of the superconducting tape is written in the equivalent circuit diagram. Since the inductance value is two orders of magnitude larger than the resistance value, the equivalent resistance part of the cable body is ignored when writing the equation, and it is combined into a matrix for solution, as shown in formula (1). For the convenience of expression, A and B are used to represent the inverse matrix of the inductance matrix and the capacitance matrix in formula (1). The inductance and capacitance matrices are shown in formulas (2) and (3) respectively.

[0058] The Kirchhoff voltage equation matrix is ​​expressed as:

[0059]

[0060] Among them, I Ai ,I Bi ,I Ci ,ISi They represent the currents of the conductive layer phase A, phase B, phase C and the shielding layer i, respectively, U Ai , U Bi , U Ci , U Si They represent the voltages of the conductive layer phase A, phase B, phase C and the i-th layer of the shielding layer respectively.

[0061]

[0062]

[0063] Among them, M represents mutual inductance and C represents capacitance.

[0064] Step 3) According to Kirchhoff's voltage equation matrix, the voltage of each phase is solved by using the current relationship between each phase current and the conductive layer and the shielding layer.

[0065] Step 3-1) Considering the three-phase AC current I containing harmonic components in the power grid A ,I B ,I C As shown in formula (4), the highest order of the harmonic component is assumed to be m.

[0066]

[0067] Among them, I k They represent the kth harmonic amplitude of the three-phase current, θ k They respectively represent the kth harmonic phase angle of the three-phase current.

[0068] Depend on Figure 2 It can be seen that the current of each phase in a multi-layer superconducting cable is divided into n layers, and the relationship between the current of each phase and its layer current is shown in formula (5):

[0069]

[0070] Among them, I Ai ,I Bi ,I Ci ,I Si They represent the currents of the conductive layer phase A, phase B, phase C and the i-th layer of the shielding layer respectively.

[0071] In order to reduce the magnetic field leakage of the superconducting cable and the electromagnetic interference of adjacent equipment, a current with the same magnitude and opposite to that of the conductive layer will flow through the shielding layer of the superconducting cable. Since the fundamental current is symmetrical in three phases, the distribution of the harmonic current in the three phases may not be symmetrical, so the current in the shielding layer is set to the opposite of the sum of the three-phase harmonic current. Since the conductive layers in each phase are in parallel, the voltage relationship can be obtained:

[0072] U A1 =UA2 =…U An

[0073] U B1 =U B2 =…U Bn

[0074] U C1 =U C2 =…U Cn

[0075] U S1 =U S2 =…U Sn

[0076] Step 3-2) According to the voltage relationship and the relationship between each phase current and its layer current, add the n-layer Kirchhoff voltage equations of each phase in the Kirchhoff voltage equation matrix (1) to obtain equation (6):

[0077]

[0078] Among them, C ab , C bc , C cs Respectively represent the capacitance between AB phases, between BC phases, between C phase and shielding layer, M ab represents the sum of the inductance values ​​within the cross-coverage range of n layers and n rows belonging to subscript a and n layers and n columns belonging to subscript b in matrix A. Subscript 1 represents phase A, subscript 2 represents phase B, subscript 3 represents phase C, and subscript 4 represents the shielding layer, that is, M 11 represents the sum of the inductance values ​​within the cross coverage of n rows and n columns belonging to n layers of phase A in matrix A, M 12 represents the sum of the inductance values ​​within the cross-coverage range of n rows belonging to n layers of phase A and n columns belonging to n layers of phase B in matrix A, M 21 It represents the sum of the inductance values ​​within the cross-coverage range of n rows belonging to n layers of phase B and n columns belonging to n layers of phase A in matrix A, and so on.

[0079] Step 3-3) For the convenience of expression, two conductive layers and one shielding layer are taken as the research structure for each phase, and the inverse matrix of the inductance matrix is Denoted as A', the capacitance matrix Denoted as B', when considering the three-phase current containing harmonic components of different orders: (i.e. ω, 3ω, 5ω, 7ω...mω (ω = 2πf)), the jω (complex frequency) part in the corresponding inductance and capacitance matrix in formula (6) also changes accordingly, so the calculation should be made according to the different order harmonics, and the 1st, 3rd...mth voltages are calculated using the following formula (7):

[0080]

[0081] Among them, I Am ,I Bm ,I Cm Respectively represent the m-order harmonic current amplitude in phase A, phase B, and phase C current, U Am , U Bm , U Cm They represent the voltages generated in the circuit by the m-order harmonic currents in the A-phase, B-phase, and C-phase currents respectively. Represents the magnitude of the shielding layer current in the case of m-order harmonic current, that is, the negative number of the sum of the conductive layer currents.

[0082] Step 4) Using the same voltage across layers in each phase, solve for the current distribution in each layer.

[0083] According to the following formula (8), the harmonic current of each layer is solved:

[0084]

[0085] Among them, I A1m ,I B1m ,I C1m They represent the current distribution of the m-order harmonic current in the first superconducting layer of the superconducting cable phase A, phase B, and phase C, respectively. A2m ,I B2m ,I C2m They represent the current distribution of the m-order harmonic current in the second superconducting layer of phase A, phase B, and phase C of the superconducting cable, respectively. Sm Represents the current distribution of the m-order harmonic current in the shielding layer of the superconducting cable

[0086] The harmonic currents of each layer obtained by solving equation (8) are superimposed to obtain the total current distribution of each layer, as shown in equation (9):

[0087]

[0088] Example 2

[0089] In order to verify the operability of the expression method of the interlayer current distribution when the multilayer superconducting cable mentioned in Example 1 of the present invention contains harmonic components, this example takes a 10kV / 2.3kA three-phase coaxial superconducting cable as an example for analysis. Each phase in the cable has two conductive layers and the outermost layer has a shielding layer. The specific parameters of the cable are shown in Table 1.

[0090] Table 1 Cable structure parameters

[0091]

[0092] In actual power grids, filters can only remove harmonics within a small frequency range and cannot completely eliminate harmonic current components. When the current waveform containing harmonic components in the power grid is known, the current waveform is digitally sampled using a sufficiently high sampling frequency; the discrete sampled current data is converted from the time domain to the frequency domain using a discrete Fourier transform or fast Fourier transform algorithm to obtain the components of each order of current in the frequency domain. In this example, it is assumed that the power grid current contains only fundamental, third-order and fifth-order harmonic currents. According to the allowable value of harmonic current when the standard voltage is 10kV in the national standard GB / T 14549-93, the amplitudes of the third harmonic and the fifth harmonic are set to 20A, and the current parameters of each phase are shown in equation (10). Solve for the current distribution when the current flows into the cable in Table 1.

[0093]

[0094] According to the superconducting cable structure data in Table 1, the inductance and capacitance values ​​in formula (1) are calculated, and the current distribution of each layer is solved through the calculation process of formula (6) to formula (9). Finally, all order currents are superimposed to obtain the total interlayer current distribution when containing harmonic components, as shown in formula (11).

[0095]

[0096] Example 3

[0097] This embodiment provides a device for calculating laminar flow distribution of a multi-layer superconducting cable taking into account the influence of harmonic currents, including a memory, a processor, and a program stored in the memory. When the processor executes the program, the method described in the above embodiment 1 is implemented.

[0098] In a preferred embodiment, the device comprises:

[0099] Equivalent circuit diagram construction module: used to construct the equivalent circuit diagram of multi-layer superconducting cables;

[0100] Voltage equation building module: used to write the Kirchhoff voltage equations for each phase and each layer for each order current component according to the equivalent circuit diagram and combine them into a matrix form;

[0101] Voltage solving module: used to solve the voltage of each phase according to Kirchhoff voltage equation matrix, using the current of each phase and the current relationship between the conductive layer and the shielding layer;

[0102] Current solution module: used to solve the current distribution of each layer by using the same voltage of each layer in each phase.

[0103] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the described module can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0104] Example 4

[0105] This embodiment provides a storage medium on which a program is stored. When the program is executed, the method described in the above embodiment 1 is implemented.

[0106] Storage media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer-readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable media does not include temporary computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0107] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for calculating laminar flow distribution of multilayer superconducting cables considering the influence of harmonic currents, characterized in that: The following steps are involved: Step 1) constructing a multilayer superconducting cable equivalent circuit diagram; Step 2) According to the equivalent circuit diagram, write the Kirchhoff voltage equations for each phase and each layer for each order current containing harmonic components and combine them into a matrix form; Step 3) According to the Kirchhoff voltage equation matrix, the voltage magnitude of each phase is solved by using the current magnitude of each phase and the current relationship between the conductive layer and the shielding layer; Step 4) using the same voltage of each layer in each phase to solve the current distribution containing harmonic components in each layer; Assume that each phase of a multi-layer superconducting cable has n conductive layers and n shielding layers. According to the equivalent circuit diagram, the current of each phase in the multi-layer superconducting cable is divided into n layers. The relationship between the current of each phase and its layer current is: I A =I A1 +I A2 +…I An I B =I B1 +I B2 +…I Bn I C =I C1 +I C2 +…I Cn I S =I S1 +I S2 +…I Sn Among them, I A ,I B ,I C Respectively represent the current of the conductive layer phase A, phase B, and phase C, I S Represents the shield current, I Ai ,I Bi ,I Ci ,I Si They represent the currents of the conductive layer phase A, phase B, phase C and the i-th layer of the shielding layer respectively; In the step 2), the equivalent resistance of the cable body is ignored when writing the Kirchhoff voltage equation for each phase and each layer; The Kirchhoff voltage equation matrix is ​​expressed as: Among them, A and B represent the inverse matrix of the inductance matrix and the capacitance matrix respectively, I Ai ,I Bi ,I Ci ,I Si They represent the currents of the conductive layer phase A, phase B, phase C and the shielding layer i, respectively, U Ai , U Bi , U Ci , U Si Represent the voltages of the conductive layer phase A, phase B, phase C and the shielding layer i respectively; Set the current in the shield layer to the inverse of the sum of the three-phase harmonic currents, and determine the voltage relationship based on the parallel relationship between the conductive layers in each phase: IN A1 =U A2 =…In An IN B1 =U B2 =…In Bn IN C1 =U C2 =…In Cn IN S1 =U S2 =…In Sn The step 3) comprises the following steps: Step 3-1) Assume that the highest order of harmonic components is m, and consider the three-phase AC current I when the power grid contains harmonic components A ,I B ,I C It is expressed as: Among them, I k They represent the kth harmonic amplitude of the three-phase current, θ k They represent the kth harmonic phase angle of the three-phase current respectively; Step 3-2) According to the voltage relationship and the relationship between each phase current and its layer current, add the n-layer Kirchhoff voltage equations of each phase in the Kirchhoff voltage equation matrix to obtain: Among them, C ab , C bc , C cs Respectively represent the capacitance between AB phases, between BC phases, between C phase and shielding layer, M ab represents the sum of the inductance values ​​within the cross-coverage range of n layers and n rows belonging to subscript a and n layers and n columns belonging to subscript b in matrix A, subscript 1 represents phase A, subscript 2 represents phase B, subscript 3 represents phase C, and subscript 4 represents the shielding layer; Step 3-3) Take two conductive layers and one shielding layer per phase as the research structure, and transform the inverse matrix of the inductance matrix Denoted as A', the capacitance matrix Denoted as B', considering the three-phase current contains harmonic components of different orders: ω, 3ω, 5ω, 7ω...mω, use the following formula to calculate the 1st, 3rd...mth voltage: Among them, I Am ,I Bm ,I Cm Respectively represent the m-order harmonic current amplitude in phase A, phase B, and phase C current, U Am , U Bm , U Cm They represent the voltages generated in the circuit by the m-order harmonic currents in the A-phase, B-phase, and C-phase currents respectively. Represents the magnitude of the shielding layer current in the case of m-order harmonic current, that is, the negative number of the sum of the conductive layer currents.

2. A method for calculating laminar flow distribution of a multilayer superconducting cable considering the influence of harmonic current according to claim 1, characterized in that: In step 4), the harmonic currents of each order in each layer are solved according to the following formula: Among them, I A1m ,I B1m ,I C1m They represent the current distribution of the m-order harmonic current in the first superconducting layer of the superconducting cable phase A, phase B, and phase C, respectively. A2m ,I B2m ,I C2m They represent the current distribution of the m-order harmonic current in the second superconducting layer of phase A, phase B, and phase C of the superconducting cable, respectively. Sm It represents the current distribution of m-order harmonic current in the shielding layer of superconducting cable.

3. A method for calculating laminar flow distribution of a multilayer superconducting cable considering the influence of harmonic current according to claim 2, characterized in that: In step 4), the harmonic currents of each layer are superimposed to obtain the total current distribution of each layer:

4. A device for calculating laminar flow distribution of a multilayer superconducting cable considering the influence of harmonic current, comprising a memory, a processor, and a program stored in the memory, characterized in that: When the processor executes the program, the method according to any one of claims 1 to 3 is implemented.

5. A storage medium having a program stored thereon, characterized in that: When the program is executed, the method according to any one of claims 1 to 3 is implemented.

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