Online monitoring method and device for ground insulation deterioration of motor winding and readable medium

Abstract

The invention relates to an on-line monitoring method and device for ground insulation deterioration of a motor winding and a readable medium. The method comprises the following steps: acquiring common-mode oscillation current of a variable frequency motor system; decomposing a high-frequency component and an intermediate-frequency component from the common-mode oscillation current by using a variational mode decomposition algorithm, and extracting a high-frequency common-mode oscillation frequency and an intermediate-frequency common-mode oscillation frequency; the degradation of the insulation state of the end part of the motor is monitored on line through the high-frequency common-mode oscillation frequency; when the internal ground insulation state of the motor winding is judged, whether the end part ground insulation of the motor is degraded or not is judged firstly, and then the degradation of the internal ground insulation state of the motor is monitored on line through the intermediate-frequency common-mode oscillation frequency according to different conditions. The method can sensitively reflect the weak change of the end part and the internal insulation of the variable frequency motor winding, and realizes the accurate on-line monitoring of the insulation state.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of motor system reliability monitoring, and in particular to an online monitoring method and device for insulation deterioration of motor winding end and internal ground and a readable medium. BACKGROUND

[0002] Motor systems are widely used in industrial automation, new energy vehicles, energy development and other fields. However, due to the influence of working environment and use conditions, motor failures are prone to occur, among which stator insulation failure accounts for more than 30% of motor failures. Once the initial failure of stator insulation occurs, it will rapidly expand, leading to equipment downtime and accidents. Therefore, it is necessary to monitor the insulation of the motor online and detect insulation degradation in the early stage.

[0003] Stator winding insulation impedance spectrum measurement is a common means of insulation monitoring, in which common-mode impedance measurement is used to evaluate the impedance characteristics of the three-phase stator winding to ground, which can effectively reflect the overall aging of the winding insulation. However, some monitoring methods based on signal injection are invasive and require an external high-frequency signal source, limiting their applicability.

[0004] Online partial discharge monitoring is also a common method, but this method is severely disturbed by noise and has low reliability, and is mainly applied to high-voltage motors above 6kV, and has limitations in the application of low-voltage variable frequency motors. In addition, although the monitoring method based on leakage current can reflect the insulation, it is difficult to effectively distinguish the deterioration position of the end and internal insulation, and the measurement accuracy is easily affected by the cable parameters in the complex common-mode electromagnetic environment of the variable frequency motor.

[0005] In recent years, research has found that insulation capacitance can be an important sign of early insulation deterioration. At the same time, in view of the strong correlation between leakage current and insulation impedance, some scholars have proposed monitoring leakage current to evaluate insulation. However, under the variable frequency power supply condition of the motor, the variable frequency converter output contains rich high-order harmonics and pulse voltage, which exerts stronger electrical stress on the winding insulation, resulting in deficiencies in accuracy and pertinence of existing monitoring methods, especially in effectively distinguishing the deterioration of the winding end and internal insulation. SUMMARY

[0006] The purpose of the present application is to provide an online monitoring method, device and readable medium for insulation deterioration of motor winding end and internal ground, which can effectively separate different modal common-mode currents, thereby realizing independent monitoring of end and internal insulation degradation.

[0007] The technical solution provided by the present application is as follows: An online monitoring method for insulation deterioration of motor winding end and internal ground, the steps of which include: S1: Collecting common-mode oscillation current of motor system ; S2: using a variational modal decomposition algorithm to decompose the common-mode current into a high-frequency common-mode current and a medium-frequency common-mode current , and then extracting a high-frequency common-mode oscillation frequency and a medium-frequency common-mode oscillation frequency ; S3: online monitoring the degree of deterioration of the motor end-to-ground insulation according to the high-frequency common-mode oscillation frequency ; if it is detected that the high-frequency common-mode oscillation frequency presents a nonlinear decline, then the motor end-to-ground insulation is deteriorated, otherwise it is not deteriorated; S4: if the motor end-to-ground insulation is not deteriorated, online monitoring the degree of deterioration of the motor internal-to-ground insulation through the medium-frequency common-mode oscillation frequency ; if it is detected that the medium-frequency common-mode oscillation frequency presents a nonlinear decline, then the motor internal-to-ground insulation is deteriorated, otherwise it is not deteriorated; S5: if the motor end-to-ground insulation is deteriorated, when the motor end insulation equivalent capacitance variation ΔC g1 and the motor winding insulation equivalent capacitance variation ΔC g2 increase, the medium-frequency common-mode oscillation frequency all present a nonlinear decline, then the motor internal-to-ground insulation is deteriorated, otherwise it is not deteriorated; S6: outputting the deterioration state of the motor winding end-to-ground and internal-to-ground insulation.

[0008] Further, the common-mode oscillation current is based on a common-mode model of a variable-frequency motor system considering cable stray parameters, and the model contains the parasitic parameters of the frequency converter, cable and motor.

[0009] Further, in the step S2, the variational modal decomposition algorithm decomposes the complex multi-modal common-mode oscillation current into a plurality of intrinsic modal functions, i.e. a high-frequency common-mode current and a medium-frequency common-mode current , each of which is centered on a center frequency; applying Hilbert transform to calculate the signal of each mode to obtain the corresponding single-sided frequency spectrum; applying the L2 norm of gradient to estimate the bandwidth, so that the sum of the estimated bandwidths of the modes is minimized, which is expressed as a constrained variational problem: wherein k is the mode number; δ(t) is the unit impulse function; by introducing Lagrange multiplier λ and quadratic penalty factor α, the modal components and the center frequency ω k can be obtained by using the multiplicative operator alternating direction method, and can be respectively expressed as: The common-mode current is decomposed into two dominant sub-modes by a variational mode decomposition algorithm, and the sub-mode functions and the center frequency are adaptively obtained The common-mode current oscillation frequency characteristics, i.e., the high-frequency common-mode oscillation frequency and the intermediate-frequency common-mode oscillation frequency

[0010] Further, in the S5, when the motor end portion ground insulation is deteriorated, the intermediate-frequency common-mode oscillation frequency is coupled to judge the deterioration of the motor internal ground insulation, which is based on the coupling relationship between the intermediate-frequency common-mode current oscillation frequency and the motor end portion insulation equivalent capacitance change ΔC g1 , the motor winding insulation equivalent capacitance change ΔC g2 , and the expression is: wherein, is the winding inductance, is the cable end cable equivalent inductance is the inter-turn capacitance, is the end portion capacitance, is the winding internal main insulation capacitance, is the ground capacitance.

[0011] An online monitoring device for motor winding end portion and internal ground insulation deterioration, characterized by comprising: a collection module for collecting the common-mode oscillation current of a variable frequency motor system ; a decomposition and extraction module for decomposing the common-mode current into a high-frequency common-mode current and an intermediate-frequency common-mode current by using a variational mode decomposition algorithm, and further extracting the high-frequency common-mode oscillation frequency and the intermediate-frequency common-mode oscillation frequency ; an end portion monitoring module for online monitoring the deterioration of the motor end portion insulation state according to the high-frequency common-mode oscillation frequency ; an internal monitoring module for judging whether the motor end portion ground insulation is deteriorated when judging the motor winding internal ground insulation state, and if the motor end portion ground insulation is not deteriorated, online monitoring the deterioration of the motor internal ground insulation state through the intermediate-frequency common-mode oscillation frequency ; and if the motor end portion ground insulation is deteriorated, coupling the intermediate-frequency common-mode oscillation frequency to judge the deterioration of the motor internal ground insulation state.

[0012] Further, the device is also used to implement the method as described above.

[0013] A computer-readable storage medium, characterized in that it includes instructions that, when executed on a device, cause the device to perform the method as described above.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides an online monitoring method, device, and readable medium for the degradation of insulation to ground at the ends and inside of motor windings. By acquiring the common-mode oscillation current of the variable frequency motor system, the common-mode current is input into a variational mode decomposition (VMD) algorithm to obtain high-frequency and medium-frequency common-mode currents. The corresponding high-frequency and medium-frequency common-mode switching oscillation frequencies are then extracted. The degradation state of the insulation to ground at the ends of the motor windings is determined by the high-frequency common-mode oscillation frequency, and the degradation state of the internal insulation to ground is determined based on the end-to-ground insulation and the medium-frequency common-mode oscillation frequency. Simultaneously, this method utilizes the modal characteristics of the common-mode current to effectively separate the influencing factors of the end and internal insulation, improving the sensitivity to identify subtle insulation changes. Therefore, this invention, by designing a monitoring scheme based on common-mode current mode decomposition, achieves separate monitoring of the end and internal insulation to ground, overcoming the limitations of traditional methods that struggle to distinguish the location of insulation degradation, are greatly affected by cable parameters, and are insensitive to subtle changes.

[0015] This method can sensitively reflect subtle changes in insulation, accurately distinguish between end and internal insulation degradation, and does not require machine shutdown. It improves the real-time performance and accuracy of monitoring, overcomes the limitations of existing methods, and is suitable for scenarios with high requirements for continuous motor operation, thus having significant engineering application value. Attached Figure Description

[0016] Figure 1. Flowchart of the online monitoring method for the insulation to ground at the end and inside of the stator winding of a variable frequency motor; Figure 2. Equivalent model diagram of common mode of motor winding; Figure 3. Deterioration of end insulation at different degrees Trend chart; Figure 4. Deterioration of internal insulation at different levels Trend chart; Figure 5. Different degrees of internal insulation degradation under the inductance of a small cable. Trend chart; Figure 6. Different degrees of insulation degradation at the lower end of the inductor and inside the winding of the large cable. Trend chart; Figure 7 Common-mode model of variable frequency motor system considering cable stray parameters; Figure 8. Path diagram of medium and high frequency common mode current in the common mode model of the variable frequency motor system with cable stray parameters; Figure 9. Time-domain diagram of high-frequency common-mode current under winding end insulation degradation in the verification experiment; Figure 10. Time-domain diagram of intermediate frequency common-mode current under winding internal insulation degradation in the verification experiment; Figure 11. Verification experiment under different degrees of insulation degradation at the winding ends Scatter plot and Theoretical estimation diagram; Figure 12 shows the results of the verification experiment under different degrees of insulation degradation inside the winding. Scatter plot and Theoretical estimation diagram; Figure 13 shows the results of verification experiments with different degrees of insulation degradation at the winding ends and inside. Change diagram; Figure 14. Schematic diagram of online monitoring device for insulation to ground at the end and inside of the stator winding of a variable frequency motor. Detailed Implementation

[0017] To better understand the purpose, technical solution, and technical effects of this invention, the invention will be further explained and described below in conjunction with the accompanying drawings and embodiments. It should also be stated that the embodiments described below are only for explaining this invention and are not intended to limit this invention.

[0018] like Figure 1 As shown in the figure, this is a flowchart of an online monitoring method for the insulation of the stator winding end and internal components of a variable frequency motor based on common-mode current variational modes, provided in an embodiment of this application. The steps include: S1. Collect the common-mode oscillation current of the variable frequency motor system through processing equipment. .

[0019] In a variable frequency motor system, the frequency converter provides voltages of different frequencies and amplitudes to achieve speed regulation of the motor. Each switching action of the frequency converter device will cause a step change in the common-mode voltage. As its load, the motor will generate a transient high-frequency common-mode oscillating current due to its own impedance characteristics.

[0020] like Figure 2 As shown, the motor common-mode equivalent model considering the coupling effect of high-frequency distributed parameters includes equivalent models of the motor windings, shaft and housing, and bearing branches. Here, W1 is the stator winding input terminal, W2 is the stator winding neutral point, F is the motor housing and grounded, and R is the shaft. C g1 C is the stray capacitance between the stator winding ends and the motor housing. g2 This refers to the stray capacitance between the inside of the motor stator winding and the motor housing. L is the equivalent resistance of the winding. cmFor the stator winding common mode inductance, in the common mode model, due to the high frequency of the stator winding inductance is much larger than the winding equivalent resistance, Can be ignored. R e For the eddy current caused by iron loss, C p For the equivalent capacitance between turns, C wr1 For the high-frequency winding and rotor stray capacitance, C wr1 And C wr2 For the low-frequency winding and rotor stray capacitance. For the shaft to the shell stray capacitance, R f For the equivalent resistance of the shaft to the bearing, And R O The equivalent oil film capacitance and resistance of the bearing. In the study of the stator common mode impedance in the MHz frequency range, the rotor and bearing part has little effect on it, and for the convenience of calculation, only the red part of the common mode model is discussed.

[0021] During the operation of the motor, the device applies a common mode voltage to the motor from the motor input terminal to the motor shell, which can generate a motor common mode current. The device will monitor the motor common mode current in real time. These data are subsequently decomposed by the variational mode decomposition (VMD) algorithm, hereinafter referred to as the VMD algorithm; and then the high-frequency component and the medium-frequency component are extracted to evaluate and analyze the winding end and internal ground insulation.

[0022] Among them, the common mode current collection method is as follows, the common mode impedance of the motor from the input terminal to the motor shell is shown in formula (1), the current flowing through the motor common mode path is shown in formula (2), and the oscillation frequency is f s As shown in formula (3): (1) (2) (3) Among them, U m (t) is the common mode voltage applied to the motor from the input terminal to the motor shell, is the corresponding motor common mode current, is the stray capacitance between the motor stator winding end and the motor shell, is the stray capacitance between the motor stator winding and the motor shell, L cm is the stator winding common mode inductance, R e is the eddy current caused by iron loss, C p is the equivalent capacitance between turns.

[0023] According to formula (2), The denominator in the expression has a pole, which is the reason for the oscillation of the common mode current through the motor. The oscillation frequency is f sAs shown in equation (3), the motor common-mode series resonance frequency is consistent with the motor common-mode series resonance frequency, and the motor common-mode series resonance frequency is consistent with the winding internal capacitance Related to the winding end-to-ground capacitance Irrelevant.

[0024] S2, the processing device decomposes the complex multi-modal common-mode oscillation current into a plurality of intrinsic mode functions (IMF), each mode concentrated on its central frequency. Then the high-frequency common-mode current and the medium-frequency mode current are decomposed from the common-mode oscillation current , and the high-frequency common-mode oscillation frequency and the medium-frequency common-mode oscillation frequency are extracted.

[0025] In the variable frequency motor system, there are rich parasitic parameters in the frequency converter, cable and motor, which provide different coupling paths for the medium and high frequency current. The common-mode voltage generated by the frequency converter is applied to the cable and motor, thereby forming a multi-modal current oscillation response. The cable stray parameters also affect the common-mode current, and the common-mode model of the variable frequency motor system considering the cable stray parameters is considered.

[0026] Wherein, the voltage U Cg1 at both ends of the motor end is related to the output common-mode voltage U CM of the frequency converter as shown in equation (4), the voltage U CM at both ends of the motor end is related to the output common-mode voltage U Cg1 of the frequency converter as shown in equation (5), and the high-frequency common-mode current flowing into the equivalent insulation capacitor at the motor end is shown in equation (6): (4) (5) (6) Then, from equation (6), the poles in the denominator are the reason for the high-frequency common-mode current oscillation, and the high-frequency common-mode current oscillation frequency is: (7) Wherein, L cm is the winding inductance, is the equivalent inductance, C p is the turn-to-turn capacitance, C g1 is the motor end capacitance, C g2 is the winding internal insulation capacitance, is the frequency converter ground capacitance, C cab1 , C cab2 is the ground capacitance.

[0027] From equation (7), the high frequency common mode oscillation frequency is related to the cable equivalent inductance , the ground capacitance C cab1 , and the motor terminal capacitance C cab2 . g1 In the long-term stable operation of the motor system, the cable stray parameters and the inverter ground capacitance parameters remain almost unchanged without any abnormality, and the motor terminal ground insulation, i.e., the equivalent capacitance of the terminal ground insulation, will directly affect the high frequency common mode oscillation frequency.

[0028] Neglecting the influence of the equivalent inductance of the common mode excitation source, the relationship between the motor terminal voltage and the common mode voltage output by the inverter is shown in equation (8), the medium frequency common mode current flowing into the motor is shown in equation (9), and the voltage division ratio of the common mode voltage output by the inverter to the motor terminal voltage is shown in equation (10): (8) (9) (10) wherein U m is the motor terminal voltage, U CM is the common mode voltage output by the inverter, is the medium frequency common mode current flowing into the motor, is the common mode impedance from the motor terminal to the motor casing, r2 is the voltage division ratio of the common mode voltage U CM output by the inverter to the motor terminal voltage U m , Z eq1 and Z eq2 correspond to the equivalent impedances shown in the figure, respectively.

[0029] Then, the medium frequency common mode current is solved, the pole of the denominator is the reason for the medium frequency common mode current oscillation, and the medium frequency common mode oscillation frequency is: (11) The medium frequency common mode oscillation frequency is affected by the motor parameters and the cable parameters, and the coupling effect of the cable resistance / motor iron loss (R / L e ) is very small, which can be ignored, and equation (11) is simplified as: (12) From equation (12), when the cable is relatively short, i.e., L <<L cm , the medium frequency common mode oscillation frequency is close to the inherent series resonance frequency of the motor, which is related to the winding inductance L cm and the inter-turn capacitance C pand winding internal insulation capacitance C g2 The longer the cable, the greater the impact of its equivalent inductance The end capacitance C g1 also affects the intermediate frequency common-mode current oscillation frequency. Therefore, the size of the cable inductance also determines the coupling relationship of the end capacitance to the intermediate frequency common-mode current oscillation frequency.

[0030] Next, the VMD algorithm can effectively decompose the complex multi-modal signal into multiple sub-signals, called intrinsic mode functions (IMF). All modes are concentrated around the center frequency, and the Hilbert transform is applied to calculate the signal of each mode ) to obtain the corresponding single-sided spectrum. Further application of the L2 norm of the gradient estimates the bandwidth, with the goal of minimizing the sum of the estimated bandwidths of each mode. The constrained variational problem is expressed as shown in equation (13): (13) where k is the mode number, δ (t) is the unit impulse function, is the mode component.

[0031] By introducing the Lagrange multiplier λ and the quadratic penalty factor α, the k mode components of the response signal decomposition are obtained by solving equation (13) using the multiplicative operator alternating direction method. The mode component ) and the center frequency ω k are represented as: (14) (15) Therefore, by decomposing the common-mode current into two dominant sub-modes using the VMD algorithm, the sub-mode function and the center frequency are adaptively obtained, and the common-mode current oscillation frequency feature , is extracted.

[0032] S3, the processing device monitors the end-to-ground insulation through the high-frequency common-mode current oscillation frequency to determine whether the motor end-to-ground insulation is deteriorating.

[0033] According to the above theoretical analysis, from equations (7) and (12), the common-mode current intermediate frequency resonance frequency and To obtain the relationship between the resonance frequency and the change in the equivalent capacitance of each insulation of the motor, equation (7) is written as an equation related to the change in the equivalent capacitance of the end insulation of the motor ΔC g1 , as shown in equation (16): (16) where Lcm For winding inductance, For equivalent inductance, For the equivalent inductance, C p For inter-turn capacitance, C g1 For the end capacitance, C g2 This is the internal insulation capacitance of the winding. According to equation (16). In ΔC g1 If the increase shows a non-linear decrease, it is considered that the insulation of the motor end to ground has deteriorated; otherwise, there is no deterioration.

[0034] Therefore, it can be obtained through variational mode decomposition algorithm. Monitoring ΔC g1 The change in the equivalent capacitance of the end insulation is used to determine the degree of degradation of the motor's end insulation. ΔC is the change in the equivalent capacitance of the end insulation. g1 Resonant frequency with high-frequency common-mode current The trend chart, such as Figure 3 As shown.

[0035] S4. If the insulation to ground at the end is not deteriorated, the processing equipment determines the internal insulation to ground.

[0036] When determining the insulation of the motor windings to ground, first determine whether the insulation of the motor ends to ground has deteriorated.

[0037] When the insulation to ground at the end deteriorates, if the cable inductance is large, the intermediate frequency common-mode oscillation frequency and ΔC g1 ΔC g2 Coupling is relevant. As shown in equation (12), the influencing factor of the intermediate frequency common-mode current resonant frequency is related to the magnitude of the cable's equivalent inductance. When the cable inductance is small, the intermediate frequency common-mode current resonant frequency is mainly affected by the equivalent capacitance of the internal insulation of the motor windings. Equation (12) can be written as the change in the equivalent capacitance ΔC within the windings. g2 The relevant equation is shown in equation (17): (17) in, This is the intermediate frequency common-mode oscillation frequency. For winding inductance, Inter-turn capacitance This refers to the internal insulation capacitor of the winding.

[0038] To determine the degree of insulation degradation inside the motor windings, the intermediate frequency common-mode oscillation frequency can be used. The change is monitored. From equation (17), it can be seen that the intermediate frequency common-mode oscillation frequency is consistent with the series resonant frequency of the motor. According to equation (17), the change in the internal insulation capacitance Δ of the winding is... Resonant frequency with intermediate frequency common-mode current The trend chart, such as Figure 4 As shown. increases, a nonlinear decrease is presented. Therefore, the degradation of the winding internal insulation can be determined by monitoring the change of ΔC increases. monitoring the change of ΔC , the degradation of the winding internal insulation can be determined.

[0039] When the cable inductance parameter is large, compared with the winding inductance, it cannot be ignored. Equation (12) is written as an equation related to ΔC g1 , ΔC g2 coupling, as shown in equation (18): (18) wherein, is the intermediate frequency common mode oscillation frequency, is the winding inductance, is the cable end cable equivalent inductance is the inter-turn capacitance, is the end capacitance, is the winding internal insulation capacitance, is the ground capacitance.

[0040] When / is very small, the change of ΔC can be ignored, only because of the change of ΔC changes. With the increase of / , the influence on ΔC becomes more and more great. According to equation (18) and the intermediate frequency common mode current resonance frequency under large cable inductance, and bivariate change trend chart, as shown in Figure 5 . Not only in increases, a nonlinear decrease is presented, but also in increases. affected by and two factors, namely, the end insulation degradation and the winding internal insulation degradation degree jointly determines .

[0041] When the end-to-ground insulation has no degradation, with the increase of the cable inductance, i.e. / , presents a nonlinear decrease, and for different cable inductance, will decrease in The increase presents a nonlinear decrease. Therefore, the variation of the internal equivalent capacitance of the motor winding under different cable parasitic inductances With The change rule determines whether insulation degradation occurs inside the winding. The variation of the internal equivalent capacitance of the motor winding under different cable parasitic inductances With The change rule is shown in the figure. Figure 6

[0042] Based on the above, first, the common-mode equivalent model of the variable frequency motor system is constructed, the common-mode current is separated by the variational mode decomposition (VMD) algorithm, and the high-frequency common-mode current and the medium-frequency common-mode current are accurately extracted. At the same time, the VMD algorithm outputs the high-frequency oscillation frequency and the medium-frequency oscillation frequency , wherein is sensitive to the change of the equivalent capacitance of the winding end-to-ground insulation, is affected by the coupling of the equivalent capacitance of the winding internal-to-ground insulation and the cable inductance . When the cable parameters are stable, the mapping relationship between the high-frequency oscillation frequency and the end insulation capacitance can directly calculate the size of through the variation of , and realize the quantitative evaluation of the end-to-ground insulation.

[0043] Then, the coupling relationship between the medium-frequency frequency and the internal insulation capacitance is established, and the cable inductance parameter is taken as a correction term to monitor the internal-to-ground insulation. The common-mode current variational mode monitoring method of the application realizes the separate monitoring of the end and internal-to-ground insulation, and overcomes the limitations of the traditional insulation monitoring method that cannot distinguish the degradation position, is greatly disturbed by the cable parameters, and is not sensitive to weak capacitance changes.

[0044] The embodiment of the application also provides a common-mode model of a variable frequency motor system with cable stray parameters, as shown in Figure 7 The model includes the parasitic parameters of the frequency converter, the cable and the motor. In the variable frequency motor system, there are rich parasitic parameters in the frequency converter, the cable and the motor, which provide different coupling paths for the medium and high frequency currents. The frequency converter of the variable frequency motor system provides voltages of different frequencies and different amplitudes to realize the speed regulation of the motor. Each switching action of the frequency converter device will bring a step change of the common-mode voltage, and the motor as its load will correspondingly generate a transient high-frequency oscillation common-mode current due to its own impedance characteristics. Among them, the cable stray parameters also affect the common-mode current.

[0045] Figure 7 ​​, the common-mode model of the variable frequency motor system considering the cable stray parameters shown in Fig. 8(a) and Fig. 8(b), and the path of the medium and high frequency common-mode current, the equivalent inductance of the cable end and the cable , the equivalent resistance , the capacitance to ground C cab1 , C cab2 The segment N of the excitation source is the reference point of the common-mode excitation source, N' is the grounding point of the frequency converter, is the grounding capacitance of the frequency converter, is the equivalent inductance of the input power grid end and the cable when the common-mode current flows back to the common-mode excitation source.

[0046] When the cable stray parameters are considered, the common-mode impedance of the variable frequency motor system has two resonance points of medium and high frequencies, which correspond to the medium frequency resonance and the high frequency resonance of the common-mode current. The motor input common-mode current considering the cable is composed of the high frequency common-mode current and the medium frequency common-mode current The high frequency common-mode current flows through the motor end capacitor without flowing into the motor winding, and the medium frequency common-mode current can penetrate into the motor winding. Due to the existence of the equivalent inductance and the grounding capacitance , U NN` is not 0. At high frequency, the capacitive reactance is much smaller than the inductive reactance, and the high frequency common-mode current flows back to the excitation source through the grounding capacitance. Correspondingly, at medium frequency, the capacitive reactance is much larger than the inductive reactance, and the medium frequency common-mode current flows back to the excitation source through the equivalent inductance .

[0047] In order to further illustrate the actual effect of the present application, the present example will verify the specific effect of the online monitoring method for the insulation between the stator winding end and the ground of the variable frequency motor through a variable frequency motor experimental system, and the verification is carried out in the form of experiment. Therefore, the specific content and steps are as follows: (1) A variable frequency motor experimental system is built. The experimental motor is a 3kW permanent magnet synchronous motor (star connection, pole pair number 5), and the bus voltage of the voltage regulator is set to 240V. A variable capacitor is connected in parallel between the winding end and the ground to simulate the end insulation degradation, and a variable capacitor is connected in parallel between the neutral point and the ground to simulate the internal insulation degradation. The common-mode current is collected by a high frequency current transformer (ETA5315, bandwidth 50MHz), and the data is recorded by a high speed oscilloscope (YOKOGAWA DL850E) and transmitted to the host computer for analysis. In this experiment, the motor common-mode parameters are obtained by sweeping frequency with an impedance analyzer (HIKO IM3570), and the cable parameters are calculated as follows: =10μH, R a =0.1Ω, =150pF; (2) A monitoring module was built, and the common-mode current was decomposed by the VMD algorithm to separate the high-frequency components. and intermediate frequency components Extract the corresponding resonant frequency and A nonlinear fitting method is established to create a mapping relationship between frequency and capacitance, ultimately achieving [the desired result]. and Quantitative estimation. Among them, Reflecting the end insulation capacitance Changes, Considering cable coupling reflects the internal insulation capacitance Changes; (3) The two current mode components of the decomposed common-mode current have resonant frequencies of 3.332 MHz and 346.5 kJ, respectively. According to formulas (8) and (13), the theoretical calculation of the oscillation frequency of the high-frequency common-mode current is 3.305 MHz and the oscillation frequency of the medium-frequency common-mode current is 344.2 kJ. The theoretical calculation results are close to the experimental values ​​(error is less than 1%), which verifies the correctness of the high-frequency common-mode circuit and medium-frequency common-mode circuit models proposed in this paper. (4) Simulate different degrees of insulation degradation at the motor ends to ground, and connect a 20~200pF capacitor in parallel between the winding end terminals and the ground. The experimental oscillation waveform of the high-frequency common-mode current is obtained by decomposing it using the VMD algorithm. From the time-domain waveform in Figure 8, it can be seen that the oscillation frequency of the high-frequency common-mode current varies with... The amplitude decreases as the value increases. The value increases with the increase of the winding. When insulation degradation does not occur at the winding ends but occurs inside the winding, a 40~520pF capacitor is connected in parallel between the winding neutral point lead-out terminal and ground. The experimental oscillation waveform of the intermediate frequency common-mode current is as follows. Figure 9 As shown in the figure, it can be seen that the oscillation frequency of the intermediate frequency common-mode current increases with... The amplitude decreases as the value increases. It increases with the increase; (5) Further analysis through comparative experiments: when both the insulation to ground at the winding ends and inside deteriorates, the effect of cable coupling should be considered. right The impact is the effectiveness of the monitoring method. Considering only... Influence , Influence For monitoring method one, considering cable coupling... right The impact is assessed using monitoring method two. An example is used to compare the accuracy of monitoring methods one and two. =200pf, =200pF, online monitoring of oscillation frequency =2.636MHz, =306.4kHz.

[0048] Based on the above steps, the experimental results are analyzed as follows: Figure 10 As shown in Tables 11 and 12. The results show that the monitoring method based on common-mode current variational mode proposed in this application, by separating frequency features through the VMD algorithm, achieves an accuracy rate exceeding 98% under different insulation degradation scenarios, and can effectively distinguish between end and internal ground insulation, exhibiting superior stability and sensitivity. Compared with methods that do not consider coupling, the accuracy is significantly improved, as shown in Table 1.

[0049] Table 1 Comparison of Winding Insulation Monitoring Methods Experiments show that the proposed method can sensitively reflect subtle changes in the insulation at the winding ends and inside the winding, solving the problems of noise interference, strong intrusion, and difficulty in distinguishing different locations of degradation in traditional monitoring methods. It is applicable to online monitoring of the insulation of variable frequency motors under different cable parameters, providing an effective means for early detection of insulation degradation.

[0050] This application also provides an online monitoring device for the insulation to ground of the stator winding ends and internal components of a variable frequency motor based on common-mode current variational modes, such as... Figure 13 As shown in the figure, this is a schematic diagram of an online monitoring device for the insulation to ground of the stator winding end and interior of a variable frequency motor based on common-mode current variational mode, provided in this application example. The device includes: Acquisition module 1 is used to acquire the common-mode oscillation current of the variable frequency motor system. The acquisition module acquires the common-mode oscillation current. It is a common-mode model of a variable frequency motor system that takes into account cable stray parameters. This model includes the parasitic parameters of the frequency converter, cable, and motor.

[0051] Decomposition and extraction module 2 is used to extract the common-mode oscillation current using the variational mode decomposition (VMD) algorithm. It is decomposed into multiple sub-signals, namely intrinsic mode functions (IMFs), with all modes concentrated at their center frequency; the Hilbert transform is applied to calculate each mode. The signal is used to obtain the corresponding one-sided spectrum; the bandwidth is estimated by applying the L2 norm of the gradient, so as to minimize the sum of the estimated bandwidths of each mode. This process is expressed as a constrained variational problem: Where k is the mode number; δ(t) is the unit impulse function. The modal components are obtained by introducing the Lagrange multiplier λ and the quadratic penalty factor α, and solving using the alternating direction method of the multiplicative operator. and center frequency , can be represented as: The common-mode current is decomposed into two dominant sub-modes by VMD, and the sub-mode functions are adaptively obtained and the center frequency , and the common-mode current oscillation frequency characteristics are extracted , .

[0052] The end monitoring module 3 is used to monitor the degradation of the motor end-to-ground insulation online according to the high-frequency common-mode oscillation frequency .

[0053] In some possible implementations, the online monitoring of the degradation of the motor end-to-ground insulation according to the high-frequency common-mode oscillation frequency is based on the relationship between the high-frequency common-mode oscillation frequency and the change amount of the equivalent capacitance of the motor end insulation, and the equation related to the change amount of the equivalent capacitance of the motor end insulation is expressed as: wherein is the equivalent inductance of the cable, , is the ground capacitance of the cable, is the ground capacitance of the frequency converter, is the stray capacitance between the motor stator winding end and the shell, and when increases, shows a nonlinear decrease.

[0054] The internal monitoring module 4 is used to first determine whether the motor end-to-ground insulation is degraded when judging the motor winding internal-to-ground insulation, and if the end-to-ground insulation is not degraded, the degradation of the motor internal-to-ground insulation is monitored online by the medium-frequency common-mode oscillation frequency ; if the end-to-ground insulation is degraded, the degradation of the motor internal-to-ground insulation is coupled to be judged by the medium-frequency common-mode oscillation frequency .

[0055] In some possible implementations, the method further includes, when the end-to-ground insulation is not degraded, the online monitoring of the degradation of the motor internal-to-ground insulation by the medium-frequency common-mode oscillation frequency is based on the relationship between the medium-frequency common-mode current oscillation frequency and the change amount of the equivalent capacitance of the winding internal insulation when the medium-frequency common-mode current oscillation frequency is less affected by the cable inductance, and the equation is expressed as: wherein, ​​​For the stator winding common mode inductance, For the inter-turn equivalent capacitance, For the motor stator winding internal and shell between the stray capacitance, when Increased, Nonlinear decline.

[0056] In some possible implementation ways, the method further comprises, when the end-to-ground insulation has deterioration, the coupling of the medium frequency common mode oscillation frequency Coupling to determine the motor internal insulation deterioration, is based on when the medium frequency common mode current oscillation frequency is greatly affected by the cable inductance, and its with 、 Coupling related relationship, expression is: Wherein, when And Increased, Nonlinear decline, through the coupling relationship to determine the internal insulation deterioration.

[0057] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it can not be understood as the limitation of the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, can make a number of deformation and improvement, these are within the scope of the present application. Therefore, the scope of the patent protection of the present application should be subject to the appended claims.

Claims

1. An online monitoring method for the degradation of insulation to ground at the ends and inside of a motor winding, comprising the following steps: S1: Acquire common-mode oscillation current of the motor system ; S2: Use variational mode decomposition algorithm to analyze the common-mode current. Decomposed into high-frequency common-mode current and intermediate frequency common mode current This allows for the extraction of the high-frequency common-mode oscillation frequency. and intermediate frequency common-mode oscillation frequency ; S3: Based on the aforementioned high-frequency common-mode oscillation frequency Online monitoring of the degree of insulation degradation to ground at the motor end; if detected If the insulation of the motor end to ground exhibits a non-linear decrease, then the insulation has deteriorated; otherwise, there is no deterioration. S4: If the insulation between the motor end and ground is not deteriorated, the intermediate frequency common-mode oscillation frequency is used. Online monitoring of the degree of insulation degradation to ground inside the motor; if the aforementioned intermediate frequency common-mode oscillation frequency is detected... If the temperature decreases non-linearly, the insulation of the motor to ground has deteriorated; otherwise, there is no deterioration. S5: If the insulation between the motor end and ground deteriorates, the change in the equivalent capacitance of the motor end insulation ΔC g1 Change in equivalent capacitance of motor winding insulation ΔC g2 When increased, the intermediate frequency common-mode oscillation frequency If all values ​​show a non-linear decrease, then the insulation of the motor to ground has deteriorated; otherwise, there is no deterioration. S6: Deterioration of the insulation to ground at the ends and inside of the output motor windings.

2. The online monitoring method for the insulation degradation to ground at the ends and inside of a motor winding as described in claim 1, characterized in that: The common-mode oscillation current It is a common-mode model of a variable frequency motor system that takes into account cable stray parameters. The model includes the parasitic parameters of the frequency converter, cable and motor.

3. The online monitoring method for the degradation of insulation to ground at the ends and inside of a motor winding as described in claim 1 or 2, characterized in that: In step S2, the variational mode decomposition algorithm decomposes the common-mode oscillation current of complex multimodes. The decomposition is divided into multiple intrinsic mode functions, namely high-frequency common-mode currents. and intermediate frequency common mode current Each mode is concentrated at its center frequency; Calculate each mode using Hilbert transform The signal is used to obtain the corresponding single-sided spectrum; The bandwidth is estimated by applying the L2 norm of the gradient, minimizing the sum of the estimated bandwidths for each mode. This can be expressed as a constrained variational problem: Where k is the mode number; δ(t) is the unit impulse function. The modal components are obtained by introducing the Lagrange multiplier λ and the quadratic penalty factor α, and solving using the alternating direction method of the multiplicative operator. and center frequency ω k , can be represented as: The common-mode current is decomposed into two dominant sub-modes using a variational mode decomposition algorithm, and the sub-mode functions are adaptively obtained. and center frequency Extract the common-mode current oscillation frequency characteristics, i.e., the high-frequency common-mode oscillation frequency. and intermediate frequency common-mode oscillation frequency .

4. The online monitoring method for the degradation of insulation to ground at the ends and inside of a motor winding as described in claim 1, characterized in that: In step S5, when the insulation of the motor end to ground deteriorates, the intermediate frequency common-mode oscillation frequency is considered. The coupling judgment of the degradation of the motor's internal insulation to ground is based on the change in the equivalent capacitance ΔC of the motor end insulation when the medium frequency common-mode current oscillation frequency is greatly affected by the cable inductance. g1 Change in equivalent capacitance of motor winding insulation ΔC g2 The coupling-related relationship is expressed as: in, For winding inductance, Cable end cable equivalent inductance Inter-turn capacitance For end capacitors, This is the main insulation capacitor inside the winding. This is the capacitance to ground.

5. An online monitoring device for the degradation of insulation to ground at the ends and inside of a motor winding, characterized in that: include, The acquisition module is used to acquire the common-mode oscillation current of the variable frequency motor system. ; The decomposition and extraction module is used to extract the common-mode current using a variational mode decomposition algorithm. Decomposed into high-frequency common-mode current and intermediate frequency common mode current This allows for the extraction of the high-frequency common-mode oscillation frequency. and intermediate frequency common-mode oscillation frequency ; End monitoring module, used to monitor the high-frequency common-mode oscillation frequency. Online monitoring of the deterioration of the insulation condition at the motor ends; The internal monitoring module, when determining the insulation status of the motor windings to ground, first checks whether the insulation at the motor ends to ground has deteriorated. If the insulation at the motor ends to ground is not deteriorated, it uses the intermediate frequency common-mode oscillation frequency... Online monitoring of the deterioration of the motor's internal insulation to ground; If the insulation between the motor end and ground is deteriorated, combined with the aforementioned intermediate frequency common-mode oscillation frequency... Coupling is used to determine the deterioration of the insulation state to ground inside the motor.

6. The online monitoring device for the degradation of insulation to ground at the ends and inside of a motor winding as described in claim 5, characterized in that: The apparatus is also used to implement the method as described in any one of claims 1-4.

7. A computer-readable storage medium, characterized in that, Includes instructions that, when executed on the device, cause the device to perform the method as described in any one of claims 1-4.

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