Voltage distribution and insulation weak point prediction method based on variable frequency motor flat wire winding

Abstract

The invention discloses a voltage distribution and insulation weak point prediction method based on a flat wire winding of a variable frequency motor, and belongs to the technical field of motor design and insulation evaluation. The method comprehensively considers the geometrical shape, the insulation structure, the working voltage and the like of a motor stator, establishes a complete finite element model of a flat wire winding motor, and improves the reliability of the motor. According to the method, distribution parameters such as capacitance, inductance and resistance of a cable and a motor winding are extracted, a winding 'I-type high-frequency equivalent circuit model is built, field-circuit coupling electromagnetic analysis is carried out by utilizing finite element simulation software, the process can be automatically realized through a compiled program, and a user only needs to provide an original motor model and working parameters, so that the method is simple and easy to implement. According to the method, the voltage distribution of the flat wire type motor winding under variable frequency driving can be efficiently and accurately predicted, the radar map capable of visually displaying the insulation weak point is generated, a new thought is provided for positioning the insulation weak point of the motor, the motor design is guided and optimized, and the evaluation efficiency and accuracy of the insulation performance of the motor are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of motor design and insulation evaluation, and in particular relates to a method for predicting voltage distribution and insulation weak points based on a flat wire winding of a variable frequency motor. Background Art

[0002] With the development of new energy electric vehicles, the power density demand of electric drive systems continues to increase, and drive motors are developing towards high speed, high frequency and high voltage. In order to further improve the power density and motor efficiency, new energy vehicles tend to use flat wire winding motors. Flat wire windings usually insert a turn of coil into the slot axially, and then transpose and weld at the end. It is favored in electric vehicle drive motors due to its high slot fill rate, good thermal conductivity and low vibration and noise. As the manufacturing process becomes more mature, the existing molding and welding equipment can meet its mass manufacturing needs.

[0003] The introduction of the third generation of wide bandgap semiconductor switching devices represented by SiC Mosfet, the increase in bus voltage levels, and the short rise time make the motor excitation have the characteristics of high voltage change gradient (dv / dt), resulting in a larger overvoltage at the three-phase input end of the motor; in addition, the high-frequency dv / dt pulse voltage can generally reach several MHz to tens of MHz. At this time, the distributed capacitance, distributed inductance and other parameters of the motor winding cannot be ignored. Due to impedance mismatch and the influence of the winding distributed parameters at high frequency, the pulse voltage is unevenly distributed inside the motor winding.

[0004] Transmission line models are often used to simulate the effects of wave propagation in inverter-fed motor windings and long motor supply cables. They are represented by lumped parameter equivalent circuits, modeled as a series of equivalent Γ-shaped or π-shaped sections. High-frequency components need to be handled by distributed parameter circuit models. These high-frequency components are considered up to a maximum frequency fmax, which is usually greater than the cutoff frequency of the FFT spectrum of the supply voltage signal. (t r is the pulse stator voltage rise time due to reflection). The minimum wavelength of the reflected waveform along the transmission line is approximately: min =v c / f max ≈ν c ·t r , where v c is the wave propagation speed. For cables, this speed is about half the speed of light in a vacuum v c ≈150m / μs. For the motor winding, due to the core lamination effect, the speed v c <75m / μs. The rise time of the pulse voltage at the motor winding input terminal is usually t r=200...300ns, at a propagation speed of 75m / μs, the minimum wavelength of the reflected electromagnetic wave is λ min ≈ν c ·t r =75m / μs·200ns=15m. When the minimum wavelength takes at least 5…10 Г-type or π-type sections, the transmission line is properly modeled. Therefore, the section length λ is obtained min / 10≈1.5m. For standard induction motors (up to 100 kW), this value is larger than the length of one turn of the winding. For larger machines (>100 kW), it is more appropriate to take several Γ-type or π-type sections for each winding.

[0005] In addition to the distribution parameters that affect the winding voltage distribution, there are a variety of winding connection structure schemes in the motor design stage, and different connection schemes will also lead to different voltage distributions. Long-term overvoltage shocks and uneven voltage distribution greatly increase the probability of premature failure of the motor insulation system during service. The turn-to-turn / phase-to-phase / to-ground voltage waveforms that the motor is subjected to during operation are as follows: Figure 4 As shown in the figure, in particular, some inter-turn / inter-phase / to-ground insulation is prone to form local high field strength. When vacuum impregnation cannot completely eliminate the air gap, partial discharge (PD) will occur with a high probability in the insulation area where the field strength is concentrated, accelerating insulation aging. Partial discharge is one of the main causes of insulation damage in variable frequency motors. In the operation of electrical equipment, partial discharge should be avoided in most cases. Therefore, in the factory inspection and acceptance test of electrical equipment, partial discharge inception voltage (PDIV) and partial discharge extinction voltage (PDEV) are two important parameters for evaluating insulation performance. Once the voltage between the motor windings exceeds its partial discharge inception voltage, it will cause rapid deterioration of the motor insulation and greatly shorten the motor service life. The inter-turn short circuit fault of the winding is the most common and most serious type of motor fault. According to statistics, the inter-turn short circuit fault of the motor accounts for about 30% to 40% of all motor faults. In order to evaluate the insulation weaknesses of the motor, the International Electrotechnical Commission (IEC) has developed corresponding standards, stipulating that PDIV tests must be performed on different insulation parts of the stator before the motor leaves the factory for operation to ensure that partial discharge (PD) does not occur under operating conditions.

[0006] In this case, it is particularly important to study the voltage distribution and insulation weaknesses of flat wire winding motors. However, the traditional voltage distribution test method mainly relies on manual testing or manual modeling and simulation. The manual test operation is complicated. The motor to be tested needs to lead out additional wires for testing. In the absence of lead wires, the insulating paint film needs to be worn to expose the copper conductor for voltage testing. In addition, manual testing is for already formed motors and cannot meet the insulation evaluation requirements of the motor design stage. For manual modeling and simulation, there are problems such as low automation, time-consuming and labor-intensive. Taking a 54-slot, 6-layer motor as an example, the complete three-phase winding high-frequency equivalent circuit is a complex network including 324 simulation units, hundreds of resistors, inductors and thousands of capacitors. In addition, the existing technology has the problems of insufficient efficiency and unintuitive results in predicting voltage distribution and locating insulation weaknesses.

[0007] In summary, in order to realize the automatic prediction of motor voltage distribution, improve the evaluation efficiency and accuracy, and meet the needs of the motor design stage, it is of great significance to develop a voltage distribution automatic prediction system; at the same time, understanding the voltage distribution law between phases and ground, between turns, and between phases of motor windings, clarifying the weak insulation points and intuitively locating them have important application value for the safe operation and optimal design of the motor. Summary of the invention

[0008] In order to solve the technical problems existing in the background technology, the present invention aims to provide a method for predicting voltage distribution and insulation weak points based on the flat wire windings of a variable frequency motor. Through this method, the voltage distribution of the motor windings can be predicted efficiently and relatively accurately. In addition, the insulation weak point locating radar map of the present invention can intuitively display the physical location of the insulation weak points of the motor.

[0009] In order to solve the technical problem, the technical solution of the present invention is:

[0010] A method for predicting voltage distribution and insulation weak points of flat wire windings of variable frequency motors, the method comprising:

[0011] S1: Based on the preset ladder circuit parameter calculation program, the number of branches and the corresponding frequency of the ladder circuit model are determined according to the number of cable layers and length, the resistance and inductance data of the cable corresponding to each branch or frequency are obtained, and the cable-to-ground capacitance data is calculated according to the distance to the ground, that is, the n-branch ladder circuit model of the cable is obtained;

[0012] S2: Perform size and shape recognition, classification and identification processing on the electrostatic field calculation model, and generate a material input interface with color identification. After the material information is input, the inter-turn capacitance and ground capacitance of the slot are automatically calculated;

[0013] S3: Perform size and shape recognition, classification and identification processing on the eddy current field calculation model, and generate a parameter input interface. After the parameter information is input, the end AC resistance and inductance values ​​are automatically calculated; the parameters include: conductor, paint film material and frequency;

[0014] S4: Number the slots and layers of the transient magnetic field model to determine whether they are consistent with the number of slots and layers in the winding arrangement diagram. If they are inconsistent, an error message is generated, that is, the stator model or the winding arrangement diagram is incorrect, please re-enter; if they are consistent, name the conductors in the transient magnetic field model one by one according to the arrangement order of the winding arrangement diagram, and assign coils to the conductors to couple the coils in the external circuit with the conductors in the magnetic field area; after the excitation setting is completed, set the boundary of the transient magnetic field model, divide the grid and add solution analysis to complete the construction of the transient magnetic field model of the flat wire winding motor;

[0015] S5: Perform secondary identification processing on the winding arrangement diagram, complete the connection of the inter-turn capacitor and the voltmeter on the basis of the high-frequency equivalent circuit of the winding, obtain a complete high-frequency equivalent circuit of the winding, integrate the cable n-branch ladder circuit obtained in step S1, and power it through a pulse source to complete the construction of the high-frequency equivalent circuit model;

[0016] S6: Obtain pulse voltage working parameters and data calculated in steps S1, S2 and S3, and generate a parameter table;

[0017] S7: importing the parameter table into the constructed high-frequency equivalent circuit, combining the transient magnetic field model of the flat wire winding motor to perform field-circuit coupling finite element analysis, and calculating the motor time domain voltage distribution;

[0018] S8: classifying the calculated time-domain voltage distribution results according to different insulation structures and extracting voltage amplitudes, and generating a voltage amplitude table for locating windings by slot number and layer number;

[0019] S9: Determine the PDIV and PDEV values ​​of the motor to be tested, and import the obtained voltage amplitude table and the measured PDIV and PDEV values ​​into the insulation weak point positioning program to generate a radar map that can intuitively display the insulation weak points of the motor, that is, realize the visualization of the voltage distribution and insulation strength of each measurement point.

[0020] Furthermore, before step S1, the method further includes:

[0021] The cable model, length, number of layers and distance to the ground, motor stator model and winding layout are obtained, and a preliminary cable n-branch ladder circuit model, electrostatic field calculation model, eddy current field calculation model, transient magnetic field model and high-frequency equivalent circuit are calculated for subsequent parameter calculation and model optimization.

[0022] Further, the step S1 specifically includes:

[0023] Before the head end of the high-frequency equivalent circuit and after the power supply, a cable model is added, including resistance, inductance and capacitance to ground parameters; the cable is represented as a combination of infinitely parallel connected concentric tubular sub-conductors, simplified to a finite number of n-branch models; for each branch, the resistance-inductance (RL) element does not change with frequency, and is connected step by step to produce an equivalent impedance, representing that the resistance and inductance of the cable change with frequency; the data set given by the proportionally spaced frequency has a good modeling effect, ensuring that the number of branches is small and the frequency dependence of R and L can be accurately represented;

[0024] The steps to obtain the cable RL parameters at different frequencies by using the CableConstants program of the EMTP platform or the finite element analysis method are as follows:

[0025] Considering the special case of the two-branch model, the model parameters are determined by formulas (1)-(6):

[0026] ΔR=R C2 -R C1 (1)

[0027] ΔL=L C1 -L C2 (2)

[0028]

[0029] Where R1, L1, R2, L2 are the resistance and inductance of the first and second branches of the model respectively; R C1 ,L C1 ,R C2 ,L C2 is the input data, which is the resistance and inductance of the cable at known frequencies ω1 and ω2. Through (1)-(6), if the RL values ​​of the cable corresponding to the two frequencies are known, the parameters of the dual-branch model can be determined analytically.

[0030] The calculation of the parameters of RL circuits with three or more branches is achieved using additional procedures for sequential circuit order simplification:

[0031] Get the two highest frequencies ω from a data set of n pairs of resistors and inductors n and ω n-1 Two pairs of related data: (R Cn ,L Cn ) and (R Cn-1 ,L Cn-1 ), and then calculate the n-branch model corresponding to the external branch (R n ,Ln ) parameters;

[0032] The equivalent circuit of the n-branch model consists of an external n-th branch and an equivalent impedance (R′ eq(ωi) and L′ eq(ωi) ), the latter represents the combination of the remaining n-1 branches at all frequencies, and the total impedance of the circuit matches the known cable data at a given frequency; therefore, the equivalent parameters of the internal branch combination are determined by formula (7) (8):

[0033]

[0034] Determine n-1 pairs of frequencies ω i After RL under (i=1,2,…n-1), the internal equivalent conductor formed by n-1 branches is fully characterized; according to the calculation steps of the nth branch, the parameters of n-1 groups of equivalent conductors are used to determine the n-1th branch, and so on. The above steps are repeated until only two data sets corresponding to frequencies are left. At this time, (5) and (6) are used to calculate the inductance and resistance parameters (R1, L1) of the first branch.

[0035] Further, the step S2 specifically includes:

[0036] Model and mesh the individual slots of the motor in the finite element platform, encrypt the mesh of the thin insulation structure to ensure the calculation accuracy, set the model boundary, and add electrostatic field solution analysis;

[0037] In the slot area, the stator core is considered as a grounded conductor "0", and the capacitance to ground between each turn and the stator core is expressed as C i.0 =C slot i.0 (i=1...n T ), n T is the total number of conductor turns in a slot, and the inter-turn capacitance is expressed as C i,j =C slot i,j ,(i≠j,j=1...n T );Consider the inter-turn capacitance C at the end ov i,j ; After simplification, the capacitance to ground of each turn is C g i.0 and the inter-turn capacitance C T i,j The calculation is as follows:

[0038]

[0039] The electrical energy method is used to calculate the capacitance of a conductor system located in a linear dielectric. For n conductors and reference ground 0, the electrical energy is written as formula (11):

[0040]

[0041] Among them C i.0 and C i,j is the capacitance of the system, u i and u j are the potentials of the i-th and j-th conductors, respectively; to determine the capacitance of a multiconductor system with n conductors and reference ground 0, we need Independent conductor potentials u of 0V and 1V i and u j The energy expression (11) is transformed into a system of equations:

[0042]

[0043] Among them, W el represents the energy vector, C represents the capacitance vector, k u Represents two vectors W el The connection matrix between and C, the capacitance can be extracted from the equations:

[0044]

[0045] Further, the step S3 specifically includes:

[0046] The end is in an irregular state due to the special torsion angle of the flat wire winding and the welding process. Therefore, 3D modeling is performed on the end. Three adjacent conductors are taken to simplify the modeling. The calculation of the AC resistance and inductance of the end is realized through the eddy current field, and the finite element method is used for analysis and calculation.

[0047] Inductance is generated by the energy of the magnetic field:

[0048]

[0049] Among them, i j and i k (j,k=1,…,n T ) is the current source of conductors j and k, which is a normalized combination of 0A and 1A sinusoidal current sources, and is introduced into the finite element partial differential equation as an initial condition;

[0050] The resistance is caused by the power dissipated:

[0051]

[0052] At high frequencies (10kHz…10MHz), the finite element method divides the model area into a large number of three-dimensional grids and uses the magnetic field energy W m and copper loss P elThe calculation method is used to continuously solve the inductance and resistance of each turn through different current combinations of 0A and 1A; finally, the inductance and AC resistance at the end are regarded as constant values ​​of equal value per turn, and the calculation result is the average of the three conductors.

[0053] Further, in step S4, the transient magnetic field model includes: a three-phase winding and a complete stator core, and the BH curve of the actual material is imported into the simulation software, fully considering the influence of the core saturation nonlinearity on the winding inductance parameters; based on finite element analysis and mesh encryption processing, the skin effect and proximity effect of the conductor at high frequency are fully considered; the inductance and resistance parameters of the conductor in the transient magnetic field model will be automatically calculated in the subsequent field-circuit coupled finite element simulation.

[0054] Further, the step S5 specifically includes:

[0055] Generate primary circuit: take each half-turn winding as a circuit unit, determine the total number of circuit units, total number of circuit units = number of slots × number of layers; connect each circuit unit in the order of winding numbers from small to large, for example, for a 54-slot motor containing UVW three-phases, the connection order is: U1i>U 1o>U 2i>U 2o……>U 54i>U 54o, V1i>V 1o>V 2i>V 2o……>V 54i>V 54o, W1i>W 1o>W 2i>W2o……>W 54i>W 54o;

[0056] Determine capacitance parameters: Identify the winding arrangement diagram, determine the position of the winding in the stator slot according to the winding arrangement diagram, and then determine the capacitance parameters corresponding to each winding unit, and assign the capacitance parameters to the corresponding circuit unit;

[0057] Remaining circuit connections: Complete the connection of the voltmeter based on the primary circuit, integrate the cable n-branch ladder circuit obtained in step S1, and power it with a pulse source to complete the construction of the high-frequency equivalent circuit model.

[0058] Further, when simulating and calculating the voltage distribution based on the flat wire winding of the variable frequency motor, the step S6 specifically includes:

[0059] The voltage distribution is simulated and calculated using Ansys Maxwell software. The basis of finite element analysis is the Maxwell equations, which consist of the following four laws: Ampere's circuit law, Faraday's law of electromagnetic induction, Gauss's flux law, and Maxwell's equations. The differential equations for electromagnetic problems using finite elements are derived, corresponding to equations (16) to (19) respectively:

[0060]

[0061] The above equations include two curl equations (16), (17) and two divergence equations (18), (19). The relationship between the field quantities E, D, B, and H is determined by the properties of the medium. For linear media, the relationship is:

[0062] D = εE (20)

[0063] B = μH (21)

[0064] J = σE (22)

[0065] Where ε is the dielectric constant of the medium, F / m; μ is the magnetic permeability of the medium, H / m; σ is the electrical conductivity of the medium, S / m; for isotropic media, ε, μ, σ are scalars; for anisotropic media, they are tensors;

[0066] To address the problem that the finite element solver will decouple the Maxwell equations, the circuit model is coupled with the finite element model through field-circuit coupling to simultaneously solve the magnetic field and electric field.

[0067] Further, the step S8 comprises:

[0068] The calculation results of the time-domain voltage distribution are obtained and exported in csv format to obtain the ungrouped raw data. The MATLAB program is used to read the groups in a loop and classify them according to different insulation structures. For each classification, a new data structure is created to store the slot number, layer number and corresponding voltage amplitude of each winding. Considering the margin of insulation evaluation, the voltage amplitude takes the maximum value within a cycle; the original data set is traversed, and the obtained voltage amplitude is integrated according to the actual position of the winding in the stator slot to generate a voltage amplitude table that can locate the specific winding by slot number and layer number.

[0069] Further, the step S9 includes:

[0070] The PDIV / PDEV test method is measured by selecting appropriate pulse voltage parameters and wiring methods according to the IEC standard using a preset PDIV / PDEV test platform;

[0071] The insulation weak point radar map generation program converts the voltage distribution results from a tabular form into a radar map that is more similar to the actual structure of the motor, and integrates each voltage amplitude into a map according to its position in the motor. Each axis of the radar map represents a slot number. The PDIV, PDEV values, and voltage distribution data of different layer numbers are distinguished by different colors or line styles. The voltage amplitude is represented by radial lines from the center to the outside. The farther away from the center, the higher the voltage amplitude. The extreme value of each axis represents the maximum and minimum voltage in the slot. Finally, by comparing the size of each voltage distribution with the PDIV test value, it is possible to analyze whether discharge occurs under general conditions. Among them, points where the voltage is distributed near or outside PDEV and PDIV can be regarded as insulation weak points of the motor.

[0072] Compared with the prior art, the advantages of the present invention are:

[0073] 1. The present invention has reasonable design, high integration, low cost and convenient operation;

[0074] 2. High evaluation efficiency: Compared with traditional experiments and testing methods, the present invention can automatically complete voltage distribution prediction and insulation evaluation, greatly shortening the evaluation cycle;

[0075] 3. The evaluation results of the insulation performance of the variable frequency motor are highly accurate: through the motor simulation modeling module, the finite element software analysis module, the external circuit generation module, etc., the present invention can more accurately predict the voltage distribution of the stator winding of the variable frequency motor under different design parameters and different working conditions, thereby providing more reliable data support for motor design and insulation evaluation;

[0076] 4. Optimize motor design: Based on the prediction results, designers can improve the structure and materials of the motor windings to improve the overall insulation performance and durability of the motor, extend the service life of the motor, and reduce the risk of accidents caused by insulation failure.

[0077] 5. Intuitively locate insulation weak points: By visualizing the winding voltage distribution according to the corresponding position in the motor as a radar chart and comparing it with the corresponding PDIV and PDEV, the present invention can more intuitively identify potential insulation weak points in the motor windings. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 , Voltage distribution prediction system diagram applicable to variable frequency drive motor flat wire winding;

[0079] Figure 2 , Four Sichuan University PDIV test platform;

[0080] Figure 3 , an example of radar diagram effect for locating insulation weak points of flat wire windings of variable frequency drive motors;

[0081] Figure 4 , the voltage waveform borne by each insulation part of the motor;

[0082] Figure 5 , the smallest unit of high-frequency equivalent circuit model. DETAILED DESCRIPTION

[0083] The specific implementation mode of the present invention is described below in conjunction with embodiments:

[0084] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification so that people familiar with this technology can understand and read them, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0085] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0086] Embodiment 1:

[0087] The embodiments further explain the present invention, as shown in the following examples. Figure 1 As shown, a method for predicting voltage distribution and insulation weak points of a variable frequency motor flat wire winding is provided, the method comprising:

[0088] S1: Obtain the cable model, length, number of layers and distance to the ground, motor stator model and winding arrangement diagram, and obtain a preliminary cable n-branch ladder circuit model, electrostatic field calculation model, eddy current field calculation model, transient magnetic field model and high-frequency equivalent circuit based on ① transmission line theory, ② 3D geometry processing software, ③ deep learning-based 3D reconstruction algorithm (using a machine to automatically extract and calculate the intrinsic features of the 3D model), ④ GFTE (a novel Graph-Neural-Network-based algorithm) based on graph neural network (GCN), and ⑤ high-frequency equivalent circuit generation program for subsequent parameter calculation and model optimization;

[0089] S2: Based on the preset ladder circuit parameter calculation program, the number of branches and the corresponding frequency of the ladder circuit model are determined according to the number of cable layers and length, the resistance and inductance data of the cable corresponding to each branch or frequency are obtained, and the cable-to-ground capacitance data is calculated according to the distance to the ground, that is, the n-branch ladder circuit model of the cable is obtained;

[0090] S3: Based on the geometric feature extraction algorithm of the contour shape (achieved by calculating and comparing the contour features of the three-dimensional model to obtain the geometric similarity of the three-dimensional model), the electrostatic field sub-model is identified, classified and marked according to the straight slot part located in the stator core, and a material input interface with color marking is generated. After the material information is input, the slot turn-to-turn capacitance and the ground capacitance value are calculated based on the finite element theory;

[0091] S4: Based on the geometric feature extraction algorithm of the contour shape, the eddy current field calculation model is subjected to size shape recognition, classification and identification processing according to the part where the end is bent and exceeds the stator core, and a parameter input interface is generated. After the parameter information is input, the end AC resistance and inductance values ​​are automatically calculated; the parameters include: conductor, paint film material and frequency;

[0092] S5: number the slots and layers of the transient magnetic field model to determine whether they are consistent with the number of slots and layers in the winding arrangement diagram. If they are inconsistent, an error message is generated, "The stator model / winding arrangement diagram is incorrect, please re-enter"; if they are consistent, name the conductors in the transient magnetic field model one by one according to the arrangement order of the winding arrangement diagram, and assign coils to the conductors, and couple the coils in the external circuit with the conductors in the magnetic field area; after the excitation setting is completed, set the boundary of the transient magnetic field model, divide the grid and add solution analysis to complete the construction of the transient magnetic field model of the flat wire winding motor;

[0093] S6: Perform secondary identification processing on the winding arrangement diagram, complete the connection of the inter-turn capacitor and the voltmeter based on the initially generated high-frequency equivalent circuit of the winding, obtain a complete high-frequency equivalent circuit of the winding, integrate the cable n-branch ladder circuit obtained in S2, and power it through a pulse source to complete the construction of the circuit part model;

[0094] S7: Obtain pulse voltage working parameters and the data obtained in steps S2, S3 and S4, and generate a parameter table;

[0095] S8: Import the parameter table into the established high-frequency equivalent circuit, perform field-circuit coupling finite element analysis in conjunction with the transient magnetic field model of the flat wire winding motor, and calculate the motor time domain voltage distribution;

[0096] S9: classifying the calculated time domain voltage distribution results according to different insulation structures (main insulation, phase-to-phase insulation, turn-to-turn insulation) and extracting voltage amplitudes, and generating a voltage amplitude table for locating windings by slot number and layer number;

[0097] S10: Determine the PDIV and PDEV values ​​of the motor to be tested, import the obtained voltage amplitude table and the measured PDIV and PDEV values ​​into the insulation weak point positioning program, and generate a radar map that can intuitively display the insulation weak points of the motor, that is, realize the visualization of the voltage distribution and insulation strength of each measurement point.

[0098] In one implementation, step S2 specifically includes:

[0099] In practice, there is a cable between the inverter and the motor. In order to simulate the actual working conditions, a cable model should be set up and added before the power supply at the head end of the high-frequency equivalent circuit, including resistance, inductance and capacitance to ground parameters. In order to include the frequency dependence of the parameters, the cable can be represented as a combination of infinitely parallel connected concentric tubular sub-conductors, each of which has a specific inductance and resistance value. In theory, it can be represented as an equivalent circuit with infinite RL branches. Since an infinite number of branches is impractical in practice, it is simplified to a finite number of "n-branch" models. For each branch, the RL element does not change with frequency and is connected step by step in a ladder manner, thereby generating an equivalent impedance representing the resistance and inductance of the cable changing with frequency. It should be noted that the more branches a cable has, the better. The best configuration is to have the least number of branches and accurately represent the frequency dependence of R and L throughout the cycle. If too many branches are used, some branch parameters may be negative, which is contrary to the equivalent resistance and inductance of the model are always positive. Studies have shown that data sets given at proportionally spaced frequencies (ω n / ω n-1 =ω n-1 / ω n-2 =…=ω2 / ω1) has a good modeling effect, and the present invention also adopts this solution.

[0100] The steps to determine the n-branch circuit parameters from the known set of cable RL parameters at different frequencies are as follows:

[0101] Considering the special case of the two-branch model, the model parameters can be determined by formulas (1)-(6):

[0102] ΔR=R C2 -R C1 (1)

[0103] ΔL=L C1 -L C2 (2)

[0104]

[0105] Where R1, L1, R2, L2 are the resistance and inductance of the first and second branches of the model respectively; R C1 ,L C1 ,R C2 ,L C2 is the input data, which is the resistance and inductance of the cable at known frequencies ω1 and ω2. Through (1)-(6), if the RL values ​​of the cable corresponding to the two frequencies are known, the parameters of the dual-branch model can be determined analytically.

[0106] If more sets of cable parameters are available, a more accurate representation can be obtained, but the parameters of RL circuits with three or more branches cannot be simply calculated using the analytical methods in (1)-(6), but require an additional procedure of sequential circuit simplification:

[0107] 1. Get the two highest frequencies ω from the data set of n pairs of resistors and inductors n and ω n-1 Two pairs of related data: (R Cn ,L Cn ) and (R Cn-1 ,L Cn-1 ), and then calculate the n-branch model corresponding to the external branch (R n ,L n ) parameters;

[0108] 2. The n-branch model equivalent circuit consists of an external n-th branch and an equivalent impedance (R′ eq(ωi) and L′ eq(ωi) ), the latter represents the combination of the remaining n-1 branches at all frequencies, and the total impedance of the circuit matches the known cable data at a given frequency. Therefore, the equivalent parameters of the internal branch combination are determined by formula (7) (8):

[0109]

[0110] 3. Determine n-1 pairs of frequencies ω i After RL under (i=1,2,…n-1), the internal equivalent conductor formed by n-1 branches is fully characterized; according to the calculation steps of the nth branch, the parameters of n-1 groups of equivalent conductors are used to determine the n-1th branch, and so on. The above steps are repeated until only two data sets corresponding to frequencies are left. At this time, (5) and (6) are used to calculate the inductance and resistance parameters (R1, L1) of the first branch.

[0111] In one implementation, step S3 specifically includes:

[0112] In the finite element platform, a slot of the motor is modeled and meshed, the mesh of the insulating structure with smaller thickness is encrypted to ensure the calculation accuracy, the model boundary is set, and the electrostatic field solution analysis is added.

[0113] Principle of distributed capacitance calculation: In the slot area, the stator core is considered as a grounded conductor "0", and the capacitance to ground between each turn and the stator core is expressed as C i.0 =C slot i.0 (i=1...n T ), n T is the total number of conductor turns in a slot, and the inter-turn capacitance is expressed as C i,j =C slot i,j ,(i≠j,j=1...n T );Consider the inter-turn capacitance C at the end ov i,j ; After simplification, the capacitance to ground of each turn is C g i.0 and the inter-turn capacitance C T i,j The calculation is as follows:

[0114]

[0115] The electrical energy method is used to calculate the capacitance of a conductor system located in a linear dielectric. For n conductors and reference ground 0, the electrical energy is written as formula (11):

[0116]

[0117] Among them C i.0 and C i,j is the capacitance of the system, u i and u j are the potentials of the i-th and j-th conductors, respectively; to determine the capacitance of a multiconductor system with n conductors and reference ground 0, we need Independent conductor potentials u of 0V and 1V i and u j The energy expression (11) is transformed into a system of equations:

[0118]

[0119] Among them, W el represents the energy vector, C represents the capacitance vector, k u Represents two vectors W el The connection matrix between and C, the capacitance can be extracted from the equations:

[0120]

[0121] In one implementation, step S4 specifically includes:

[0122] The end is irregular due to the special torsion angle of the flat wire winding and the welding process. 3D modeling of the end is selected. To simplify the modeling, three adjacent conductors are taken. The calculation of the AC resistance and inductance of the end is realized through the eddy current field. The actual inductance and resistance are not constant, but depend on the frequency. Therefore, the finite element method is used for analysis and calculation.

[0123] Inductance is generated by the energy of the magnetic field:

[0124]

[0125] where i j and i k , j=1,…,n T and k=1,…,n T , is the current source of conductors j and k, which is a normalized combination of 0A and 1A sinusoidal current sources, and is introduced into the finite element partial differential equation as an initial condition;

[0126] The resistance is caused by the power dissipated:

[0127]

[0128] At high frequencies (10kHz…10MHz), the finite element method divides the model area into a large number of three-dimensional grids and uses the magnetic field energy W m and copper loss P el The calculation method is used to continuously solve the inductance and resistance of each turn through different current combinations of 0A and 1A; finally, the inductance and AC resistance at the end are regarded as constant values ​​of equal value per turn, and the calculation result is the average of the three conductors.

[0129] In one embodiment, the winding arrangement diagram specifically includes:

[0130] The winding arrangement diagram provides the position information, connection scheme and transposition method of the motor winding turn by turn, and distinguishes different phases by different colors. Explanation of the numbers: For example, for a 54-slot motor containing three phases UVW, the element "blue 30i" in the 4th column and 6th row in the winding arrangement diagram represents that the 30th winding unit of the U phase is located in the 6th layer of the 4th slot of the motor, and the current direction is positive; the element "red 35o" in the 4th column and 5th row represents that the 35th winding unit of the W phase is located in the 5th layer of the 4th slot of the motor, and the current direction is negative;

[0131] The function of the winding arrangement diagram is to provide the numbering basis for the transient magnetic field model described in S5; and to provide the wiring method of the winding part of the high-frequency equivalent circuit.

[0132] In one implementation, step S5 specifically includes:

[0133] The transient magnetic field model includes all three-phase windings and a complete stator core, and imports the BH curve of the actual material into the simulation software, fully considering the influence of the core saturation nonlinearity on the winding inductance parameters; based on finite element analysis and mesh encryption processing, the skin effect and proximity effect of the conductor at high frequency are fully considered; the inductance and resistance parameters of the conductor in the transient magnetic field model will be calculated automatically in the subsequent field-circuit coupled finite element simulation, and there is no need to add them to the parameter table.

[0134] In one implementation, the high-frequency equivalent circuit specifically includes:

[0135] ①Construct circuit unit model based on transmission line theory: The transmission line model is usually used to simulate the wave propagation effect in the inverter-powered motor winding and the long motor power supply cable. It is represented by a distributed parameter equivalent circuit and is modeled as a series of equivalent Γ-type or π-type sections. Each half-turn winding is a circuit unit. The equivalent circuit model of a single-turn winding is as follows: Figure 5 As shown, where u i (i=1,2,…) is the node voltage of the i-th unit, i i is the current flowing through the i-th unit; the distribution parameter is T i Including the self-inductance L of the straight part i and AC resistance R i , M 1,2 is the mutual inductance between the straight parts; the concentrated parameters include distributed capacitance, AC resistance and inductance at the ends, C i0 is the capacitance to ground for each unit, which is grounded through the stator core; C i,m is the inter-turn capacitance between adjacent windings; R ei and L ei The AC resistance and inductance at the ends are respectively. From the above analysis, it can be seen that the distributed parameters required to establish a high-frequency equivalent circuit include: turn-to-turn capacitance and ground capacitance, AC resistance and inductance parameters at the ends, and AC resistance and inductance parameters at the straight part. Assuming that the motor has n flat wire windings, that is, it contains 2n units, Kirchhoff's current law gives:

[0136]

[0137] According to Kirchhoff's voltage law:

[0138]

[0139] From formula (18), we can get the differential equation RI+Z(dI / dt)=U, where:

[0140] R=[R1+R e1 , …,R m+R em ,…,R 2n +R e2n ] (19)

[0141] I=[i1,…,i m ,…,i 2n ] (20)

[0142] Z is the winding inductance matrix, and the main diagonal line is the self-inductance (L i +L ei ), mutual inductance M i,m At the (i,m) position, i and m are determined according to the winding connection structure.

[0143] ② Calculate the total number of circuit units and generate a primary circuit containing only winding modules: total number of circuit units = number of slots × number of layers. Connect each circuit unit in the order of winding numbers from small to large to obtain three independent phase winding modules UVW. Since in each SVPWM non-zero vector state, the three-phase winding is always connected in series with two phases and then in parallel with another phase, this connection method is also used to connect the three phase winding modules UVW, recorded as UV / / W;

[0144] ③ Supplement the primary circuit: Determine the position of the winding in the stator slot according to the winding layout diagram, and then determine the capacitance parameters corresponding to each winding unit, traverse all adjacent windings in the same slot, obtain the connection method of the inter-turn capacitance, connect all the inter-turn capacitances to the existing primary circuit, and then add the voltmeter to the circuit turn by turn to measure the voltage distribution. The final complete high-frequency equivalent circuit consists of four parts: winding, voltmeter, cable and power supply.

[0145] In one implementation, step S8 specifically includes:

[0146] The software used in the voltage distribution simulation calculation is Ansys Maxwell, which is a comprehensive electromagnetic simulation software suitable for designing and analyzing 3D / 2D structures such as motors, drives, transformers and other electrical and electromechanical equipment. Based on the finite element method (FEM), Maxwell can solve static, frequency domain and time-varying electromagnetic and electric fields. The basis of the field-path coupled finite element calculation is the Maxwell equations, which actually consists of four laws, namely: Ampere's loop law, Faraday's law of electromagnetic induction, Gauss's electric flux law and Gauss's magnetic flux law (also known as the law of flux continuity). Regardless of the distribution of the medium and the magnetic field strength H, the line integral of the magnetic field strength along any closed path in the magnetic field is equal to the sum of the currents passing through the surface Ω determined by the integral path, or the line integral is equal to the total current surrounded by the integral path. The current here includes conduction current (generated by free charge) and displacement current (generated by electric field changes), and its mathematical expression is as shown in formula (21), which is called Ampere's loop law.

[0147]

[0148] Faraday's law of electromagnetic induction states that the induced electromotive force in a closed loop is proportional to the rate of change of the magnetic flux passing through the loop with time, which can be expressed as an integral (22):

[0149]

[0150] Regardless of the distribution of the electrolyte and the electric flux density vector in the electric field, the electric flux passing through any closed surface is equal to the amount of charge enclosed by the closed surface. It is pointed out here that the electric flux is also the integral of the electric flux density vector on this closed surface. This is called Gauss's law of electric flux. The integral form of this law can be expressed as follows:

[0151]

[0152] In a magnetic field, no matter how the medium and the magnetic flux density vector are distributed, the magnetic flux passing through any closed surface is always equal to zero. Here, it is pointed out that the magnetic flux is the directed integral of the magnetic flux vector on this closed surface. The integral form of Gauss's flux law is:

[0153]

[0154] Equations (21) to (24) constitute the Maxwell equations describing the electromagnetic field, which are expressed in integral form. In addition, they also have their own differential form, through which differential equations that can be used to deal with electromagnetic problems using finite elements can be derived, corresponding to equations (25) to (28) respectively:

[0155]

[0156] The above equations contain two curl equations (25), (26) and two divergence equations (27), (28). The relationship between the field quantities E, D, B, and H is determined by the properties of the medium. For linear media, the relationship is:

[0157] D=εE(29)

[0158] B=μH(30)

[0159] J = σE (31)

[0160] Where ε is the dielectric constant of the medium, F / m; μ is the magnetic permeability of the medium, H / m; σ is the electrical conductivity of the medium, S / m; for isotropic media, ε, μ, σ are scalars; for anisotropic media, they are tensors.

[0161] To address the problem that the finite element solver will decouple the Maxwell equations, the circuit model can be coupled with the finite element model through field-circuit coupling to solve the magnetic field and electric field simultaneously.

[0162] In one implementation, step S9 specifically includes:

[0163] The calculation results of the time domain voltage distribution are obtained and exported in csv format to obtain the ungrouped raw data. The MATLAB program is used to read the groups in a loop and classify them according to different insulation structures (main insulation, phase-to-phase insulation, turn-to-turn insulation). For each classification, a new data structure (such as DataFrame) is created to store the slot number, layer number and corresponding voltage amplitude of each winding. Considering the margin of insulation evaluation, the voltage amplitude takes the maximum value within a cycle. The original data set is traversed, and the obtained voltage amplitude is integrated according to the actual position of the winding in the stator slot to generate a voltage amplitude table that can locate the specific winding by slot number and layer number.

[0164] In one embodiment, step S10 includes:

[0165] The PDIV / PDEV test method: According to the IEC standard, select appropriate pulse voltage parameters and wiring methods, using Figure 2 The voltage distribution results were measured by the Sichuan University PDIV / PDEV test platform shown in the figure; the insulation weak point radar map generation program converts the voltage distribution results from a table form into a radar map that is more similar to the actual structure of the motor, and integrates each voltage amplitude into a map according to its position in the motor, which is more intuitive. Figure 3As shown, each axis of the radar chart represents a slot number. The PDIV, PDEV values, and voltage distribution data of different layer numbers are distinguished by different colors or line styles. The voltage amplitude is represented by radial lines from the center to the outside. The farther away from the center, the higher the voltage amplitude. The extreme value of each axis represents the maximum and minimum voltage in the slot. Finally, by comparing the size of each voltage distribution with the PDIV test value, it is possible to analyze whether discharge occurs under general conditions. Among them, points where the voltage is distributed near or outside PDEV and PDIV can be regarded as weak insulation points of the motor.

[0166] Embodiment 2:

[0167] This embodiment 2 is applied to embodiment 1, and is a description of the expansion during use by the user, and is applicable to the specific implementation method of the voltage distribution prediction system of the flat wire winding of the variable frequency drive motor. First, the user imports the cable model, length, number of layers and distance to the ground, the motor stator model and the winding arrangement diagram into the input module. The system preliminarily generates the cable "n" branch ladder circuit model according to the cable model, extracts the electrostatic field calculation model and eddy current field calculation model for calculating the winding distribution parameters according to the motor stator model, and establishes the flat wire winding motor transient magnetic field model in combination with the winding arrangement diagram, and establishes the three-phase winding high-frequency equivalent circuit model according to the winding arrangement diagram. After the required model is generated, the system prompts the user to enter the information such as materials and frequencies required to calculate the distribution parameters. After the user completes the input, the calculation automatically starts, and the calculated cable, winding distribution parameter values ​​and the input working voltage parameters are summarized in the parameter table. Finally, the parameter table is imported into the established high-frequency equivalent circuit, and the field-circuit coupling finite element analysis is performed in conjunction with the motor transient magnetic field model to calculate the motor voltage distribution.

[0168] like Figure 3 , which is applicable to the specific implementation method of the radar diagram for locating insulation weak points of the flat wire winding of the variable frequency drive motor. According to the IEC standard, select the appropriate pulse voltage parameters and wiring method, and use Figure 2 The Sichuan University PDIV test platform shown in the figure measures the PDIV and PDEV values ​​of the motor to be tested. Finally, the calculated voltage distribution results and the measured PDIV and PDEV values ​​are imported into the insulation weak point positioning program to generate a radar chart that can intuitively display the insulation weak points of the motor and visualize the voltage distribution and insulation strength of each measurement point.

[0169] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0170] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0171] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0172] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention.

[0173] Many other changes and modifications may be made without departing from the concept and scope of the present invention.It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for predicting voltage distribution and insulation weak points of flat-wire windings of variable-frequency motors, characterized in that: The method comprises: S1: Based on the preset ladder circuit parameter calculation program, the number of branches and the corresponding frequency of the ladder circuit model are determined according to the number of cable layers and length, the resistance and inductance data of the cable corresponding to each branch or frequency are obtained, and the cable-to-ground capacitance data is calculated according to the distance to the ground, that is, the n-branch ladder circuit model of the cable is obtained; S2: Perform size and shape recognition, classification and identification processing on the electrostatic field calculation model, and generate a material input interface with color identification. After the material information is input, the inter-turn capacitance and ground capacitance of the slot are automatically calculated; S3: Perform size and shape recognition, classification and identification processing on the eddy current field calculation model, and generate a parameter input interface. After the parameter information is input, the end AC resistance and inductance values ​​are automatically calculated; the parameters include: conductor, paint film material and frequency; S4: Number the slots and layers of the transient magnetic field model to determine whether they are consistent with the number of slots and layers in the winding arrangement diagram. If they are inconsistent, an error message is generated, that is, the stator model or the winding arrangement diagram is incorrect, please re-enter; if they are consistent, name the conductors in the transient magnetic field model one by one according to the arrangement order of the winding arrangement diagram, and assign coils to the conductors to couple the coils in the external circuit with the conductors in the magnetic field area; after the excitation setting is completed, set the boundary of the transient magnetic field model, divide the grid and add solution analysis to complete the construction of the transient magnetic field model of the flat wire winding motor; S5: Perform secondary identification processing on the winding arrangement diagram, complete the connection of the inter-turn capacitor and the voltmeter on the basis of the high-frequency equivalent circuit of the winding, obtain a complete high-frequency equivalent circuit of the winding, integrate the cable n-branch ladder circuit obtained in step S1, and power it through a pulse source to complete the construction of the high-frequency equivalent circuit model; S6: Obtain pulse voltage working parameters and data calculated in steps S1, S2 and S3, and generate a parameter table; S7: importing the parameter table into the constructed high-frequency equivalent circuit, combining the transient magnetic field model of the flat wire winding motor to perform field-circuit coupling finite element analysis, and calculating the motor time domain voltage distribution; S8: classifying the calculated time-domain voltage distribution results according to different insulation structures and extracting voltage amplitudes, and generating a voltage amplitude table for locating windings by slot number and layer number; S9: Determine the PDIV and PDEV values ​​of the motor to be tested, and import the obtained voltage amplitude table and the measured PDIV and PDEV values ​​into the insulation weak point positioning program to generate a radar map that can intuitively display the insulation weak points of the motor, that is, realize the visualization of the voltage distribution and insulation strength of each measurement point.

2. The voltage distribution and insulation weak point prediction method based on the flat wire winding of the variable frequency motor according to claim 1 is characterized in that: Before step S1, the method further includes: The cable model, length, number of layers and distance to the ground, motor stator model and winding layout are obtained, and a preliminary cable n-branch ladder circuit model, electrostatic field calculation model, eddy current field calculation model, transient magnetic field model and high-frequency equivalent circuit are calculated for subsequent parameter calculation and model optimization.

3. The method for predicting voltage distribution and insulation weak points based on flat wire windings of variable frequency motors according to claim 1, characterized in that: The step S1 specifically includes: Before the head end of the high-frequency equivalent circuit and after the power supply, a cable model is added, including resistance, inductance and capacitance to ground parameters; the cable is represented as a combination of infinitely parallel connected concentric tubular sub-conductors, simplified to a finite number of n-branch models; for each branch, the resistance-inductance RL element does not change with frequency, and is connected step by step to produce an equivalent impedance, representing that the resistance and inductance of the cable change with frequency; the data set given by proportionally spaced frequencies has a good modeling effect, ensuring that the number of branches is small and the frequency dependence of R and L can be accurately represented; The steps to obtain the cable RL parameters at different frequencies by using the CableConstants program of the EMTP platform or the finite element analysis method are as follows: Considering the special case of the two-branch model, the model parameters are determined by formulas (1)-(6): ΔR=R C2 -R C1 (1) ΔL=L C1 -L C2 (2) Where R1, L1, R2, L2 are the resistance and inductance of the first and second branches of the model respectively; R C1 ,L C1 ,R C2 ,L C2 is the input data, which is the resistance and inductance of the cable at known frequencies ω1 and ω2. Through (1)-(6), if the RL values ​​of the cable corresponding to the two frequencies are known, the parameters of the dual-branch model can be determined analytically. The calculation of the parameters of RL circuits with three or more branches is achieved using additional procedures for sequential circuit order simplification: Get the two highest frequencies ω from a data set of n pairs of resistors and inductors n and ω n-1 Two pairs of related data: (R Cn , L Cn ) and (R Cn-1 , L Cn-1 ), and then calculate the n-branch model corresponding to the external branch (R n , L n ) parameters; The equivalent circuit of the n-branch model consists of an external n-th branch and an equivalent impedance (R′ eq(ωi) and L′ eq(ωi) ), the latter represents the combination of the remaining n-1 branches at all frequencies, and the total impedance of the circuit matches the known cable data at a given frequency; therefore, the equivalent parameters of the internal branch combination are determined by formula (7) (8): Determine n-1 pairs of frequencies ω i After RL under (i=1,2,...n-1), the internal equivalent conductor formed by the n-1 branches is fully characterized; according to the calculation steps of the n-th branch, the parameters of the n-1 groups of equivalent conductors are used to determine the n-1th branch, and so on. The above steps are repeated until only two data sets corresponding to the frequencies are left. At this time, (5) and (6) are used to calculate the inductance and resistance parameters (R1, L1) of the first branch.

4. The voltage distribution and insulation weak point prediction method based on the flat wire winding of the variable frequency motor according to claim 1, characterized in that: The step S2 specifically includes: Model and mesh the individual slots of the motor in the finite element platform, encrypt the mesh of the thin insulation structure to ensure the calculation accuracy, set the model boundary, and add electrostatic field solution analysis; In the slot area, the stator core is considered as a grounded conductor "0", and the capacitance to ground between each turn and the stator core is expressed as C i.0 =C slot i.0 (i=1…n T ), n T is the total number of conductor turns in a slot, and the inter-turn capacitance is expressed as C i，j =C slot i，j , (i≠j, j=1…nT); consider the inter-turn capacitance C at the end ov i，j ; After simplification, the capacitance to ground of each turn is C g i.0 and the inter-turn capacitance C T i，j The calculation is as follows: The electrical energy method is used to calculate the capacitance of a conductor system located in a linear dielectric. For n conductors and reference ground 0, the electrical energy is written as formula (11): Among them C i.0 and C i，j is the capacitance of the system, u i and u j are the potentials of the i-th and j-th conductors, respectively; to determine the capacitance of a multiconductor system with n conductors and reference ground 0, we need Independent conductor potentials u of 0V and 1V i and u j The energy expression (11) is transformed into a system of equations: Among them, W el represents the energy vector, C represents the capacitance vector, k u Represents two vectors W el The connection matrix between and C, the capacitance can be extracted from the equations:

5. The voltage distribution and insulation weak point prediction method based on the flat wire winding of the variable frequency motor according to claim 1, characterized in that: The step S3 specifically includes: The end is in an irregular state due to the special torsion angle of the flat wire winding and the welding process. Therefore, 3D modeling is performed on the end. Three adjacent conductors are taken to simplify the modeling. The calculation of the AC resistance and inductance of the end is realized through the eddy current field, and the finite element method is used for analysis and calculation. Inductance is generated by the energy of the magnetic field: Among them, i j and i k (j, k = 1, ..., n T ) is the current source of conductors j and k, which is a normalized combination of 0A and 1A sinusoidal current sources, and is introduced into the finite element partial differential equation as an initial condition; The resistance is caused by the power dissipated: At high frequencies, the finite element method divides the model region into a large number of three-dimensional grids and uses the magnetic field energy W m and copper loss P el The calculation method is used to continuously solve the inductance and resistance of each turn through different current combinations of 0A and 1A; finally, the inductance and AC resistance at the end are regarded as constant values ​​of equal value per turn, and the calculation result is the average of the three conductors.

6. The voltage distribution and insulation weak point prediction method based on the flat wire winding of the variable frequency motor according to claim 1, characterized in that: In step S4, the transient magnetic field model includes: three-phase windings and a complete stator core, and the BH curve of the actual material is imported into the simulation software, fully considering the influence of the core saturation nonlinearity on the winding inductance parameters; based on finite element analysis and mesh encryption processing, the skin effect and proximity effect of the conductor at high frequency are fully considered; the inductance and resistance parameters of the conductor in the transient magnetic field model will be automatically calculated in the subsequent field-circuit coupled finite element simulation.

7. The voltage distribution and insulation weak point prediction method based on the flat wire winding of the variable frequency motor according to claim 1, characterized in that: The step S5 specifically includes: Generate primary circuit: take each half-turn winding as a circuit unit, determine the total number of circuit units, total number of circuit units = number of slots × number of layers; connect each circuit unit in the order of winding numbers from small to large, for example, for a 54-slot motor containing UVW three-phases, the connection order is: U1i>U 1o>U 2i>U 2o……>U 54i>U 54o, V1i>V 1o>V 2i>V2o……>V 54i>V 54o, W1i>W 1o>W 2i>W2o……>W 54i>W 54o; Determine capacitance parameters: Identify the winding arrangement diagram, determine the position of the winding in the stator slot according to the winding arrangement diagram, and then determine the capacitance parameters corresponding to each winding unit, and assign the capacitance parameters to the corresponding circuit unit; Remaining circuit connections: Complete the connection of the voltmeter based on the primary circuit, integrate the cable n-branch ladder circuit obtained in step S1, and power it with a pulse source to complete the construction of the high-frequency equivalent circuit model.

8. The method for predicting voltage distribution and insulation weak points based on flat wire windings of variable frequency motors according to claim 1, characterized in that: When simulating and calculating the voltage distribution based on the flat wire winding of the variable frequency motor, the step S6 specifically includes: The voltage distribution is simulated and calculated using Ansys Maxwell software. The basis of finite element analysis is the Maxwell equations, which consist of the following four laws: Ampere's circuit law, Faraday's law of electromagnetic induction, Gauss's flux law, and Maxwell's equations. The differential equations for electromagnetic problems using finite elements are derived, corresponding to equations (16) to (19) respectively: The above equations include two curl equations (16), (17) and two divergence equations (18), (19). The relationship between the field quantities E, D, B, and H is determined by the properties of the medium. For linear media, the relationship is: D = εE (20) B = μH (21) J = σE (22) Where ε is the dielectric constant of the medium, F / m; μ is the magnetic permeability of the medium, H / m; σ is the electrical conductivity of the medium, S / m; for isotropic media, ε, μ, σ are scalars; for anisotropic media, they are tensors; To address the problem that the finite element solver will decouple the Maxwell equations, the circuit model is coupled with the finite element model through field-circuit coupling to simultaneously solve the magnetic field and electric field.

9. The method for predicting voltage distribution and insulation weak points based on flat wire windings of variable frequency motors according to claim 1, characterized in that: The step S8 comprises: The calculation results of the time-domain voltage distribution are obtained and exported in csv format to obtain the ungrouped raw data. The MATLAB program is used to read the groups in a loop and classify them according to different insulation structures. For each classification, a new data structure is created to store the slot number, layer number and corresponding voltage amplitude of each winding. Considering the margin of insulation evaluation, the voltage amplitude takes the maximum value within a cycle; the original data set is traversed, and the obtained voltage amplitude is integrated according to the actual position of the winding in the stator slot to generate a voltage amplitude table that can locate the specific winding by slot number and layer number.

10. The voltage distribution and insulation weak point prediction method based on the flat wire winding of the variable frequency motor according to claim 1, characterized in that: The step S9 comprises: The PDIV / PDEV test method is measured by selecting appropriate pulse voltage parameters and wiring methods according to the IEC standard using a preset PDIV / PDEV test platform; The insulation weak point radar map generation program converts the voltage distribution results from a tabular form into a radar map that is more similar to the actual structure of the motor, and integrates each voltage amplitude into a map according to its position in the motor. Each axis of the radar map represents a slot number. The PDIV, PDEV values, and voltage distribution data of different layer numbers are distinguished by different colors or line styles. The voltage amplitude is represented by radial lines from the center to the outside. The farther away from the center, the higher the voltage amplitude. The extreme value of each axis represents the maximum and minimum voltage in the slot. Finally, by comparing the size of each voltage distribution with the PDIV test value, it is possible to analyze whether discharge occurs under general conditions. Among them, points where the voltage is distributed near or outside PDEV and PDIV can be regarded as insulation weak points of the motor.

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