CN114611055A - Modeling method for conducted electromagnetic interference of motor driving system of electric vehicle - Google Patents

Abstract

The invention provides a method for modeling conducted electromagnetic interference of a motor driving system of an electric vehicle, which provides a complete modeling mode for fully considering parasitic parameters of all parts of a motor controller, a motor, a busbar and a cable and electromagnetic disturbance generating factors aiming at the motor driving system of the electric vehicle, overcomes various defects existing in the prior art, can achieve a good electromagnetic conducted interference simulation effect in a wider frequency range based on the model obtained by the invention, and has high model accuracy and wider applicability.

Description

Modeling method for conducted electromagnetic interference of motor driving system of electric vehicle

Technical Field

The invention belongs to the technical field of electromagnetic interference (EMI) modeling, and particularly relates to a conducted electromagnetic interference modeling method for a motor driving system of an electric automobile.

Background

The motor controller is used as a key component of a new energy automobile, when the motor controller works, the inverter high-power semiconductor devices (such as IGBT and the like) are operated to be quickly switched on and off to generate transient current and transient voltage, and because various parasitic parameters exist in the system, the conduction emission and radiation emission of electromagnetic disturbance can be formed, so that how to restrain negative influence caused by electromagnetic interference (EMI) is a great challenge in the design of a motor driving system of the current electric automobile. In order to verify the effectiveness and feasibility of the EMI suppression technology, a relatively accurate electromagnetic interference prediction model of the motor drive system needs to be established, so as to predict and evaluate EMI at the initial stage of product design and guide the electromagnetic compatibility design of the system.

At present, the modeling methods of the motor driving system mainly include a full wave method, a partial unit equivalent circuit method, a model order reduction method and the like. The full-wave electromagnetic modeling method is accurate in calculation, but due to the fact that the structures of the motor and the inverter are complex, a large amount of calculation time and a large amount of memory are needed for application of the full-wave model. The partial cell equivalent circuit (PEEC) method requires hundreds or thousands of elements to represent a simple geometric body, and is not suitable for modeling a complex structure. Model reduction (MOR) techniques can be used for system equivalent circuit modeling, but cannot analyze the effects of system internal parasitic parameters on EMI. Meanwhile, the extraction of the high-frequency parasitic parameters of the system elements is very important for establishing a conducted electromagnetic interference model, and the prediction accuracy of the model is directly influenced. The current methods mainly include Finite Element Method (FEM) and curve fitting method. The equivalent circuit established based on the FEM is accurate, but has high complexity, high calculation difficulty and long time consumption, and is not suitable for engineering application. The curve fitting method is simple, but the established circuit model has no obvious correlation with the motor structure, and main elements of the motor causing electromagnetic interference cannot be found. Therefore, the existing EMI modeling methods have certain defects and cannot meet the requirements of the field of new energy automobiles.

Disclosure of Invention

In view of the above, aiming at the technical problems in the prior art, the invention provides a modeling method for conducted electromagnetic interference of a motor driving system of an electric vehicle, which specifically comprises the following steps:

step 1, selecting a proper element, and initially establishing an electric vehicle driving system model topology consisting of a direct current bus, a direct current cable, a motor controller, a motor, an alternating current bus and an alternating current cable which are sequentially cascaded;

step 2, neglecting the distribution parameters of the direct-current busbar and the alternating-current busbar, and respectively establishing corresponding high-frequency parasitic parameter models only by using the concentration parameters and combining a busbar equivalent circuit;

step 3, aiming at the motor controller, establishing a collector-emitter interelectrode capacitance C aiming at the IGBT module of the motor controller_CEImpedance Z with positive pole to neutral point_UPNegative electrode to neutral point impedance Z_UNAnd positive to negative impedance Z_PNUModel relationship between them, and the positive-electrode-to-ground impedance Z of the IGBT module_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_UAnd IGBT module parasitic parameters: positive electrode capacitance to ground C_PGNegative electrode-to-ground capacitor C_NGAnd neutral point to ground capacitance C_UGThe model relationship between them; performing a motor controller part modeling for measuring the impedance Z_UP、Z_UN、Z_PNAnd Z_P、Z_N、Z_UCan respectively output each parasitic parameter C of the IGBT module_CEAnd C_PG、C_NG、C_UG；

Step 4, respectively measuring single-phase earth impedance and three-phase earth impedance of the motor, namely common mode impedance, and single-phase earth impedance of the motor, namely differential mode impedance; establishing a capacitance C to ground with the motor winding based on the common-mode impedance_GA model relationship therebetween; obtaining a model relation between the frequency-impedance curve resonance impedance peak and a motor single-phase winding RLC equivalent unit based on the frequency-impedance curve resonance impedance peak of the differential mode impedance;

step 5, measuring the impedance of a single cable with the length of 1m aiming at the alternating current cable, neglecting mutual inductance and mutual capacitance between two phases and establishing a three-phase alternating current cable model; and aiming at the direct current cable, measuring the impedance of a single cable with the length of 2m and establishing a direct current cable model. The modeling of the whole electric automobile motor driving system conducted electromagnetic interference is completed through the steps.

Further, it is characterized byThe capacitor C_CEAnd positive electrode impedance to ground Z_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_UThe relationship between them is derived by the following steps:

neglecting the capacitance to ground of the IGBT module, the capacitance C_CEAnd positive pole to neutral point impedance Z of IGBT module_UPNegative electrode to neutral point impedance Z_UNAnd positive to negative impedance Z_PNHas the following relationship:

thereby respectively obtaining the capacitance C of the positive electrode to the neutral point_UPNegative electrode to neutral point capacitor C_UNPositive to negative capacitance C_PN：

Connecting the positive pole of the IGBT module to the ground_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_URespectively expressed as:

the equivalent capacitance C of the IGBT module to the earth_PNegative electrode-to-ground equivalent capacitor C_NAnd neutral point to ground equivalent capacitance C_URespectively as follows:

thereby by measuring Z_P、Z_N、Z_UThen the C can be obtained_PG、C_NG、C_UG。

Further, the motor winding single-phase model in the step 4 consists of three groups of cascaded RLC parallel resonance units;

considering 6 curve regions divided by the first three resonant impedance spikes for the frequency-impedance curve of the differential mode impedance, and sequentially performing the following steps:

firstly, selecting frequencies of two points and corresponding impedances in an inductive area of a first peak with the frequency less than the minimum frequency point, and calculating a main inductance L of a winding_m：

In the formula (f)_P1、Z₁And f_P2、Z₂The frequencies and corresponding impedances at two points on the curve of the region are shown.

② calculating a first peak frequency point f₁Corresponding capacitance C of_m：

From the first peak frequency point f₁Determining the parasitic resistance of the main winding according to the peak amplitude;

thirdly, calculating a first trough frequency point f₂Inductance L of₁+L₂：

Fourthly, the second peak frequency point f₃And a second valley frequency point f₄Calculating the inductance L₁And L₂The proportion of (A):

fifthly, the second peak frequency point f₃And the third sharp peak frequency point f₅Calculating the capacitance C₁And C₂：

From the second peak frequency f₃And the third sharp peak frequency point f₅Determining corresponding parasitic resistances respectively according to the peak amplitudes; using the measured frequency f_P3Common mode impedance Z of₃Calculating the grounding capacitance C of the motor winding_GThe value of (c):

further, in the modeling, a direct-current bus supporting capacitor and an alternating-current bus supporting capacitor are respectively arranged between the direct-current bus and an IGBT module of the motor controller and between the IGBT module and the alternating-current bus for balancing bus voltage and eliminating ripples.

The modeling method for the conducted electromagnetic interference of the motor driving system of the electric automobile provided by the invention provides a complete modeling mode for fully considering the parasitic parameters of all parts of the motor controller, the motor, the busbar and the cable and the electromagnetic disturbance generating factors aiming at the motor driving system of the electric automobile, and overcomes various defects in the prior art.

Drawings

FIG. 1 is a single bridge arm IGBT high frequency equivalent model implemented by the present invention;

FIG. 2 is an equivalent impedance calculation circuit between the ports of the IGBT module provided by the invention;

FIG. 3 is an equivalent impedance calculation circuit of the IGBT module port to ground provided by the invention;

FIG. 4 is a high frequency equivalent model of the DC bus and the AC bus according to the present invention;

FIG. 5 is a high frequency equivalent model of a DC bus support capacitor implemented in accordance with the present invention;

FIG. 6 is a high frequency equivalent model of a motor controller embodying the present invention;

FIG. 7 is an impedance magnitude-frequency curve of a single-phase winding of the motor provided by the present invention;

FIG. 8 illustrates a single-phase winding model of an electrical machine embodying the present invention;

FIG. 9 is a high frequency equivalent model of a three-phase motor winding embodying the present invention;

FIG. 10 is a high frequency equivalent model of a DC cable and an AC cable implemented in accordance with the present invention;

FIG. 11 is a high frequency equivalent model of a motor drive system embodying the present invention;

fig. 12 is a comparison of modeling simulation and experimental test curves of a high-frequency equivalent model of a motor driving system implemented by the invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a modeling method for conducting electromagnetic interference of a motor driving system of an electric automobile, which specifically comprises the following steps:

step 1, selecting a proper element, and preliminarily establishing an electric vehicle driving system model topology composed of a direct current bus, a direct current cable, a motor controller, a motor, an alternating current bus and an alternating current cable which are sequentially cascaded;

step 2, neglecting the distribution parameters of the direct-current busbar and the alternating-current busbar, and respectively establishing corresponding high-frequency parasitic parameter models only by using the concentration parameters and combining a busbar equivalent circuit;

step 3, aiming at the motor controller, establishing a collector-emitter interelectrode capacitance C aiming at the IGBT module of the motor controller_CEImpedance Z with positive pole to neutral point_UPNegative electrode to neutral point impedance Z_UNAnd positive to negative impedance Z_PNUModel relationship between them, and the positive-electrode-to-ground impedance Z of the IGBT module_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_UAnd IGBT module parasitic parameters: positive electrode capacitance to ground C_PGNegative electrode-to-ground capacitor C_NGAnd neutral point to ground capacitance C_UGThe model relationship between them; performing a motor controller partial modeling for measuring the impedance Z_UP、Z_UN、Z_PNAnd Z_P、Z_N、Z_UCan respectively output each parasitic parameter C of the IGBT module_CEAnd C_PG、C_NG、C_UG；

Step 4, respectively measuring single-phase earth impedance and three-phase earth impedance of the motor, namely common mode impedance, and single-phase earth impedance of the motor, namely differential mode impedance; establishing a capacitance C to ground with the motor winding based on the common-mode impedance_GThe model relationship between them; obtaining a model relation between the frequency-impedance curve resonance impedance peak and a motor single-phase winding RLC equivalent unit based on the frequency-impedance curve resonance impedance peak of the differential mode impedance;

step 5, measuring the impedance of a single cable with the length of 1m aiming at the alternating current cable, neglecting mutual inductance and mutual capacitance between two phases and establishing a three-phase alternating current cable model; and aiming at the direct current cable, measuring the impedance of a single cable with the length of 2m and establishing a direct current cable model. The modeling of the whole electric automobile motor driving system conducted electromagnetic interference is completed through the steps.

In a preferred embodiment of the invention, four parasitic capacitances are considered for the IGBT module of a single leg as shown in fig. 1: collector-emitter interelectrode capacitance C_CEPositive electrode-to-ground capacitor C_PGNegative electrode-to-ground capacitor C_NGAnd neutral point to ground capacitance C_UG. In general, C_CEHas a capacitance value of about several tens nF, and a capacitance to ground C_PG、C_UG、C_NGIs in the order of a few hundred pF, so the capacitance to ground C of the IGBT module is ignored_UG. Using vector network analyzer, respectively aligning IGBT modules (type: IGBT)FS800R07A2E3) equivalent impedance.

Respectively obtaining positive pole to neutral point impedance Z through impedance measurement between ports_UPNegative electrode to neutral point impedance Z_UNPositive to negative impedance Z_PN. Establishing impedance Z from positive pole of IGBT module to neutral point_UPNegative electrode to neutral point impedance Z_UNAnd positive to negative impedance Z_PNThe calculating circuits (2) are shown in FIGS. 2(a), (b), and (c), respectively. According to the analysis of the equivalent impedance calculation circuit, the following results are obtained:

calculating to obtain equivalent capacitance C_UPAnd C_UNHas a capacitance value of 23nF, C_PNAnd 11.5 nF. :

calculating to obtain C_CEAnd 23 nF. (ii) a

And respectively obtaining the positive pole earth impedance, the negative pole earth impedance and the neutral point earth impedance through the measurement of the port earth impedance. Establishing positive earth impedance Z of IGBT module_PNegative electrode impedance to ground Z_NAnd neutral-to-ground impedance Z_UThe calculating circuits (2) are shown in FIGS. 3(a), (b), and (c), respectively. Connecting the positive pole of the IGBT module to the ground_PNegative electrode impedance to ground Z_NAnd neutral-to-ground impedance Z_URespectively expressed as:

calculating to obtain equivalent capacitance C_P≈1.2272nF，C_N≈1.2029nF，C_U≈1.2429nF。

The equivalent capacitance C of the IGBT module to the earth_PNegative electrode-to-ground equivalent capacitor C_NAnd a neutral point-to-ground equivalent capacitance C_URespectively as follows:

calculating to obtain C_PG＝480pF，C_NG＝240pF，C_UG＝540pF。

Thereby by measuring Z_P、Z_N、Z_UThen the C can be obtained_PG、C_NG、C_UG。

And establishing a three-dimensional model of the direct-current busbar and the alternating-current copper busbar shown in the figure 4 by using software ANSYS/Q3D, and extracting high-frequency parasitic parameters. Since the dc bus bar and the ac bus bar have short lengths, only lumped parameter models are created as shown in fig. 4(a) and (b). Wherein L is_BPIs self-inductance of the positive copper bar, L_BNFor self-inductance of the negative copper bar, M_PNFor mutual inductance of positive and negative copper bars, C_BPIs a positive electrode copper bar capacitor to ground C_BNIs a ground capacitor of the negative copper bar, C_PNIs a capacitance between the positive and negative copper bars, L_BUIs self-inductance of U-phase copper bar, L_BVIs self-inductance of the V-phase copper bar, L_BWSelf-inductance of W-phase copper bar, C_BUIs a ground capacitor, C of the U-phase copper bar_BVIs a ground capacitor of V-phase copper bar, C_BWIs a W-phase copper bar earth capacitance.

The direct-current bus supporting capacitor is arranged between the direct-current copper bar and the IGBT module and used for smoothing bus voltage and eliminating bus ripples. The parasitic inductance and the parasitic capacitance of the support capacitor are obtained by adopting the same measurement and calculation method of the IGBT module, and a high-frequency equivalent circuit model of the direct-current bus support capacitor shown in figure 5 is established.

After connecting the IGBT module model, the dc bus bar model, the ac bus bar model, and the dc bus bar support capacitor model, the high-frequency equivalent model of the motor controller may be as shown in fig. 6. The main parameters are shown in table 1:

TABLE 1 high-frequency model parameter table of motor controller

In step 4, a vector network analyzer is used to measure the impedance of the motor between single phase and three phase (i.e. common mode impedance) and between single phase and two phase and single phase (differential mode impedance) respectively. There are three resonance peaks in the port differential mode impedance curves of the motor U-phase and W-phase windings, as shown in fig. 7. The single-phase model of the motor winding is composed of three groups of cascaded RLC parallel resonance units, as shown in FIG. 8.

Considering 6 curve regions divided by the first three resonant impedance spikes for the frequency-impedance curve of the differential mode impedance, and sequentially performing the following steps:

firstly, selecting frequencies of two points and corresponding impedances in an inductive area of a first peak with the frequency less than the minimum frequency point, and calculating a main inductance L of a winding_m：

In the formula (f)_P1、Z₁And f_P2、Z₂The frequencies and corresponding impedances at two points on the curve of the region are shown. L can be calculated by selecting two points of (30kHz, 13 omega) and (200kHz, 85 omega)_m＝67μH。

② first peak frequency point f₁The spike at 450kHz frequency point is caused by the main inductance L of the winding_mAnd a capacitor C_mCaused by resonance, C can be calculated according to the following formula_mCalculating the first peak frequency f at 1.8nF₁The corresponding capacitance of (C) can be obtained_m＝1.8nF：

Wherein the parasitic resistance of the main winding is related to the amplitude of the resonance point, R_m＝310Ω；

③ first wave trough frequency point f₂The trough at the frequency point of 1.1MHz is formed by C_mAnd an inductance L₁And L₂Caused by resonance, calculatingFirst trough frequency point f₂The inductance of can be L₁+L₂＝113nH：

Fourthly, the second peak frequency point f₃46MHz and a second valley frequency f₄Calculating the inductance L at 100MHz₁And L₂The proportion of (A):

can be calculated to obtain: l is₁＝97nH，L₂＝16nH。

Due to C₁And L₁The resonance forms a second peak frequency point f₃Peak at 46MHz, C₂And L₂The resonance forms a third peak frequency point f₅Peak at 166MHz, so C₁And C₂Can calculate the capacitance C from the second peak and the third peak, respectively₁And C₂：

According to the second peak frequency point f₃46MHz and third sharp peak frequency point f₅Peak amplitude at 166MHz can be found: r₁＝350Ω，R₂＝150Ω。

Using the measured frequency f_P3Common mode impedance Z of₃Calculating the grounding capacitance C of the motor winding_GThe value of (c):

frequency point f can be selected in the frequency range of three phases to the ground of 10kHz-1MHz_P3Common mode impedance Z measured at 100kHz₃120 omega, the grounding capacitance C of the motor winding is calculated_G＝13.2nF。

The high-frequency equivalent circuit model of the permanent magnet synchronous motor is shown in fig. 9, and the element parameters in the model are shown in table 2. In the frequency range of 10kHz-200MHz, the deviation between the simulation result and the experimental result of the motor common mode equivalent impedance is small, and the established motor common mode impedance equivalent circuit model is relatively accurate.

TABLE 2 model parameters of PMSM

The method comprises the steps of establishing a high-frequency equivalent circuit model of a high-voltage cable with the length of 1m for the cable by adopting a measuring and calculating method similar to modeling of a permanent magnet synchronous motor, carrying out simulation test, and proving that the accuracy of the high-frequency equivalent circuit model of the cable is higher because the deviation between a cable impedance simulation result and a test result is smaller. Because the vehicle high-voltage power cables are all shielded wires, mutual inductance and mutual capacitance between different wires can be ignored. Therefore, from the model of the single cable, a three-phase alternating current cable model as shown in fig. 10(a) can be established. And by measuring the impedance of a 2m single cable, a high voltage direct current cable model can be established in the same way, as shown in fig. 10 (b).

The high-frequency equivalent circuit model of the motor driving system is composed of the established subsystem models, the models are established in ANSYS/Simplorer, the motor control module is established in Matlab software, and driving signals of 6 IGBT tubes are provided, as shown in FIG. 11. Through the collaborative simulation of Matlab and ANSYS software, the prediction of the transmission disturbance of the motor driving system can be realized.

In the specific implementation of the invention, the conducted emission test was carried out under the rated operating condition (53Nm 1900rpm) of the motor 1/4 with reference to the standard GB/T36282-2018. The comparison of the simulation result and the experiment result is shown in fig. 12, and it can be seen that the simulation result and the experiment result are good in correspondence within the frequency range of 150kHz to 108MHz, the error of the simulation result below 30MHz is less than 10dB, the accuracy of the high-frequency equivalent circuit model of the motor driving system is high, and the high-frequency equivalent circuit model can be used for simulating the conduction emission of the actual motor driving system.

It should be understood that, the sequence numbers of the steps in the embodiment of the present invention do not mean the execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiment of the present invention.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (4)

1. A modeling method for conducted electromagnetic interference of a motor driving system of an electric automobile is characterized by comprising the following steps: the method specifically comprises the following steps:

step 1, selecting a proper element, and preliminarily establishing an electric vehicle driving system model topology composed of a direct current bus, a direct current cable, a motor controller, a motor, an alternating current bus and an alternating current cable which are sequentially cascaded;

step 2, neglecting the distribution parameters of the direct-current busbar and the alternating-current busbar, and respectively establishing corresponding high-frequency parasitic parameter models only by using the concentration parameters and combining a busbar equivalent circuit;

step 3, aiming at the motor controller, establishing a collector-emitter interelectrode capacitance C aiming at the IGBT module of the motor controller_CEImpedance Z with positive pole to neutral point_UPNegative electrode to neutral point impedance Z_UNAnd positive to negative impedance Z_PNUModel relationship between them, and the positive-electrode-to-ground impedance Z of the IGBT module_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_UAnd IGBT module parasitic parameters: positive electrode capacitance to ground C_PGNegative electrode-to-ground capacitor C_NGAnd neutral point to ground capacitance C_UGThe model relationship between them; complete the motor controller partFractional modeling for measuring the impedance Z_UP、Z_UN、Z_PNAnd Z_P、Z_N、Z_UCan respectively output each parasitic parameter C of the IGBT module_CEAnd C_PG、C_NG、C_UG；

Step 4, respectively measuring single-phase earth impedance and three-phase earth impedance of the motor, namely common mode impedance, and single-phase earth impedance of the motor, namely differential mode impedance; establishing a capacitance C to ground with the motor winding based on the common-mode impedance_GThe model relationship between them; obtaining a model relation between the frequency-impedance curve resonance impedance peak and a motor single-phase winding RLC equivalent unit based on the frequency-impedance curve resonance impedance peak of the differential mode impedance;

step 5, measuring the impedance of a single cable with the length of 1m aiming at the alternating current cable, neglecting mutual inductance and mutual capacitance between two phases and establishing a three-phase alternating current cable model; and aiming at the direct current cable, measuring the impedance of a single cable with the length of 2m and establishing a direct current cable model.

2. The method of claim 1, wherein: the capacitor C_CEAnd positive electrode impedance to ground Z_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_UThe relationship between them is derived by the following steps:

neglecting the capacitance to ground of the IGBT module, the capacitance C_CEAnd positive pole to neutral point impedance Z of IGBT module_UPNegative electrode to neutral point impedance Z_UNAnd positive to negative impedance Z_PNHas the following relationship:

thereby respectively obtaining the positive electrode to neutral point capacitance C_UPNegative electrode to neutral point capacitor C_UNPositive to negative capacitance C_PN：

Connecting the positive pole of the IGBT module to the ground_PNegative electrode impedance to ground Z_NAnd neutral point to ground impedance Z_URespectively expressed as:

the equivalent capacitance C of the IGBT module to the earth_PNegative electrode-to-ground equivalent capacitor C_NAnd neutral point to ground equivalent capacitance C_URespectively as follows:

thereby by measuring Z_P、Z_N、Z_UThen the C can be obtained_PG、C_NG、C_UG。

3. The method of claim 1, wherein: the motor winding single-phase model in the step 4 consists of three groups of cascaded RLC parallel resonance units;

considering 6 curve regions divided by the first three resonant impedance spikes for the frequency-impedance curve of the differential mode impedance, and sequentially performing the following steps:

firstly, selecting frequencies of two points and corresponding impedances in an inductive area of a first peak with the frequency less than the minimum frequency point, and calculating a main inductance L of a winding_m：

In the formula, f_P1、Z₁And f_P2、Z₂The frequencies and corresponding impedances at two points on the curve of the region are shown.

② calculating the first peak frequencyPoint f₁Corresponding capacitance C of_m：

From the first peak frequency point f₁Determining the parasitic resistance of the main winding according to the peak amplitude;

thirdly, calculating a first trough frequency point f₂Inductance L of₁+L₂：

Fourthly, the second peak frequency point f₃And a second valley frequency point f₄Calculating the inductance L₁And L₂The proportion of (A):

fifthly, the second peak frequency point f₃And the third sharp peak frequency point f₅Calculating the capacitance C₁And C₂：

From the second peak frequency f₃And the third sharp peak frequency point f₅Determining corresponding parasitic resistances respectively according to the peak amplitudes;

using the measured frequency f_P3Common mode impedance Z of₃Calculating the grounding capacitance C of the motor winding_GThe value of (c):

4. the method of claim 1, wherein: in modeling, a direct-current bus supporting capacitor and an alternating-current bus supporting capacitor are respectively arranged between the direct-current bus and an IGBT module of a motor controller and between the IGBT module and the alternating-current bus for balancing bus voltage and eliminating ripples.

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