Turn-to-turn insulation degradation monitoring method based on winding impedance spectrum division

Abstract

The invention relates to the technical field of permanent magnet synchronous motor fault monitoring, and discloses a turn-to-turn insulation degradation monitoring method based on winding impedance spectrum division, which establishes a lumped parameter model of a stator winding, analyzes winding impedance spectrum division for insulation state monitoring on the basis of the lumped parameter model, and provides a turn-to-turn insulation degradation monitoring method based on the winding impedance spectrum division. Then, the influence of turn-to-turn insulation degradation on different areas of the winding impedance spectrum is verified, a transient current response based on impedance spectrum division is provided to extract turn-to-turn insulation monitoring indexes, and then a determination method for analyzing qualified PWM excitation is provided. According to the method, the frequency domain sensitive to the turn-to-turn insulation degradation is divided in the impedance spectrum, a direct corresponding relation is established between the turn-to-turn insulation degradation and the transient current response, and the insulation degradation is monitored through the transient current response.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnet synchronous motor fault monitoring, and in particular to a turn-to-turn insulation degradation monitoring method based on winding impedance spectrum division. Background Art

[0002] The insulation system of inverter-fed motors (IFMS, variable frequency motors) is constantly subjected to various aging stresses during operation and gradually ages. Especially with the popularization of wide bandgap devices in inverters, higher dv / dt and switching frequency have greatly accelerated this process. The switching transient response method is a common method for inverter motor stator insulation monitoring in recent years. It can detect insulation degradation at an early stage, thereby preventing serious insulation failures.

[0003] However, in the above method, the relationship between the phase current transient response and the turn-to-turn insulation degradation cannot be determined in the turn-to-turn insulation monitoring, so the insulation aging degree of the motor cannot be accurately monitored.

[0004] Due to the weak degradation characteristics of inter-turn insulation, monitoring its early degradation is difficult and is considered one of the main research gaps in low-voltage and medium-voltage motors. Although existing methods use the amplitude change of the frequency band centered on the parallel resonance point of the transient current transient response to detect the inter-turn insulation condition, the different variation trends of the winding impedance and the switching transient current response spectrum in different ranges, which are sensitive to inter-turn insulation degradation, are not explained in detail. On the other hand, the switching transient response is directly affected by the inverter PWM voltage excitation mode, which may change dynamically with the working conditions of I FMs. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and to design a method for monitoring the deterioration of inter-turn insulation based on the division of winding impedance spectrum.

[0006] To achieve the above-mentioned purpose, the technical solution of the present invention is a method for monitoring inter-turn insulation degradation based on winding impedance spectrum division, comprising:

[0007] Establish a high-frequency stator winding model and determine the sensitive areas of different impedance spectra for inter-turn insulation degradation;

[0008] Establish analytical links between turn-to-turn insulation degradation and corresponding sensitive regions in winding impedance and switching transient current response spectra;

[0009] The inter-turn insulation monitoring index is extracted from the transient current response based on impedance spectrum division, and qualified PWM voltage excitation is obtained.

[0010] In the high frequency stator winding model, C g1 and C g2They are the equivalent capacitance between the winding end coil and the stator core, and between the neutral line and the stator core respectively; C g1 With C g2 The sum is the equivalent capacitance of the stator winding and the stator core at low frequency; C t is the capacitive coupling effect in the stator winding; R e is the loss equivalent resistance; R is the winding resistance; L d is the winding inductance.

[0011] The process of determining the different impedance spectrum sensitive areas is as follows:

[0012] Determine the impedance Z of single-phase winding to ground based on high-frequency stator winding model PG for:

[0013]

[0014] In the formula, Z PG Determined by the test frequency and model parameters, the inter-turn insulation capacitance C t Depending on the configuration, shape and material of the insulation system, the capacitance C t Will change, C t It increases with the increase of inter-turn insulation degradation;

[0015] Z PG Amplitude vs. C t The partial derivative of is:

[0016]

[0017] in,

[0018]

[0019]

[0020] Where K is always positive;

[0021] Solving equation (2), we can obtain the positive and negative values ​​of partial derivatives in different frequency bands:

[0022]

[0023] In formula (5), the boundary frequencies f1 and f2 can be calculated according to (4)-(6) combined with the model parameters, and the different impedance spectrum sensitive areas are determined by dividing f1 and f2.

[0024] The extraction process of the turn-to-turn insulation monitoring index is as follows:

[0025] The spectrum of the transient current response is expressed as I(g), where g represents the discrete frequency order and the sampling rate F is used. s and the sample size Ns Calculate the corresponding frequency f g , as shown below:

[0026]

[0027] The inter-turn insulation monitoring index in different impedance spectrum sensitive areas is defined as IIMI1 p,k and IIMI2 p,k

[0028]

[0029] Where, p is the p-phase winding, p=A,B,C; K is K th Switching event; f1 and f2 are the boundary frequencies of the above impedance spectrum division;

[0030] Inter-turn insulation monitoring index IIMI p The expression is:

[0031]

[0032] where m is the number of switching events.

[0033] The PWM voltage excitation selects a rising edge of the PWM voltage under a positive load current or a falling edge of the PWM voltage under a negative load current as a qualified PWM voltage excitation.

[0034] Compared with the prior art, this application has the following advantages:

[0035] 1. This application uses a high-frequency model of the motor stator winding to theoretically determine the different impedance spectrum sensitive areas of inter-turn insulation degradation, and establishes an analytical connection between inter-turn insulation degradation and the corresponding sensitive areas in the winding impedance and switching transient current response spectrum;

[0036] 2. This application determines the qualified PWM voltage excitation when I FMs are operating normally, which greatly improves the reliability of the monitoring results;

[0037] 3. This application does not require additional signal injection equipment, is non-invasive, and is easy for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a principle diagram of a method for monitoring inter-turn insulation degradation based on winding impedance spectrum division according to the present invention;

[0039] Figure 2 It is a flow chart of impedance area division boundary calculation according to the present invention;

[0040] Figure 3 It is a high-frequency model diagram of the stator single-phase winding of the present invention;

[0041] Figure 4 is the PWM voltage rise time (t r ) and the switching transient current response (I amp )Amplitude statistics chart;

[0042] Figure 5 is a switch transition diagram of a half-bridge inverter with positive current polarity according to the present invention; in the figure, (a) t <t1,(b)t1<t<t2,(c)t2<t<t3,(d)t> t3;

[0043] Figure 6 is an output voltage diagram of the half-bridge inverter when the load current is (a) positive or (b) negative according to the present invention;

[0044] Figure 7 is the PWM voltage rise time (t r ) and fall time (t f ) statistical chart. DETAILED DESCRIPTION

[0045] The present invention will be described in detail below in conjunction with the accompanying drawings. Figure 1-7 As shown;

[0046] The research on switching transient characteristics is mainly focused on the frequency range from several hundred kHz to several MHz. Therefore, the modeling of stator winding only considers its high-frequency characteristics. The lumped parameter single-phase high-frequency winding model of PMSM (permanent magnet synchronous motor) is as follows: Figure 3 As shown, among which C g1 and C g2 They are the equivalent capacitance between the winding end coil and the stator core, and between the neutral line and the stator core respectively; C g1 With C g2 The sum is the equivalent capacitance of the stator winding and the stator core at low frequency; C t is the capacitive coupling effect in the stator winding; R e is the loss equivalent resistance; R is the winding resistance; L d is the winding inductance. R can be ignored because it is less important than the winding inductance (ωL) in the high frequency band. d ) is much smaller.

[0047] In order to obtain accurate monitoring indicators, it is necessary to identify different areas in the winding impedance spectrum that are sensitive to interturn insulation degradation. Figure 3 From the model shown, it can be seen that the impedance of a single-phase winding to ground is Z PG for

[0048]

[0049] ZPG Determined by the test frequency and model parameters. Turn-to-turn insulation capacitance C t Depending on the configuration, shape and material of the insulation system, the capacitance C t Will change, C t As the degree of inter-turn insulation degradation increases. t Yes|Z PG |, we derived Z PG Amplitude vs. C t The partial derivative of is shown below

[0050]

[0051] in,

[0052]

[0053] K is always positive. The sign of the above partial derivative determines C t When changing |Z PG |The trend of change. Solving equation (2), we can further deduce that the positive and negative partial derivatives of different frequency bands are

[0054]

[0055] The boundary frequencies f1 and f2 can be calculated based on (4)-(6) combined with the model parameters. Therefore, the impedance of the single-phase winding to ground can be divided into three regions, and the influence of inter-turn insulation degradation on the impedance amplitude in different regions is different. In region 1 where the frequency is lower than f1 and region 3 where the frequency is higher than f2, the impedance amplitude decreases with the inter-turn insulation degradation because Z PG C t The partial derivative of is negative. Existing studies have shown that the inter-turn capacitance begins to affect the winding impedance only in a relatively high frequency range. Therefore, in region 1, the effect of inter-turn insulation on the impedance can be ignored because the impedance in this region is mainly determined by the GW insulation (ground wall insulation). On the other hand, at frequencies between f1 and f2 in region 2, the impedance amplitude increases with the severity of degradation. In region 3, where the frequency is higher than f2, the impedance amplitude decreases. The impedance region division boundary calculation process is as follows Figure 2 shown.

[0056] It has been verified that as the degree of degradation increases, the upper frequency f2 of region 2 decreases. As the severity of degradation increases, the negative ΔZ (impedance change, normalized with the health state value, recorded as ΔZ) of the impedance spectrum in region 2 increases, but the positive ΔZ increases more, so the overall ΔZ increases. However, if region 2 is used for insulation monitoring, the weakening effect of the increased degree of degradation on the monitoring index becomes obvious. In region 3, the impedance amplitude continues to decrease as the severity of degradation increases. Therefore, the indicators established in region 3 can more accurately monitor insulation degradation of different degrees of severity.

[0057] For installed motors, using current is more convenient than measuring winding impedance from a condition monitoring perspective. The switching transient current response is determined by the PWM voltage as a high-frequency excitation and the stator winding as a load, and the impedance change of the winding caused by the degradation of the inter-turn insulation can be extracted from the transient current response. Therefore, the corresponding frequency components in the transient current response can be extracted based on the impedance spectrum partition to evaluate the inter-turn insulation condition.

[0058] According to the above analysis, as the severity of degradation increases, for frequencies between f1 and f2 in region 2, the winding impedance amplitude increases, so the amplitude of the corresponding frequency component in the current response will decrease; for frequencies above f2 in region 3, the winding impedance amplitude decreases, and the amplitude of the corresponding frequency component in the current response increases. The spectrum of the transient current response is represented as I(g), where g represents the discrete frequency order, and the sampling rate F is used. s and the sample size N s Calculate the corresponding frequency f g , as shown below:

[0059]

[0060] Two inter-turn insulation monitoring indicators based on area 2 and area 3 are defined as IIMI1 and IIMI2, respectively. p,k and IIMI2 p,k

[0061]

[0062] Where, p is the p-phase winding, p=A,B,C; K is K th Switching event; f1 and f2 are the boundary frequencies of the above impedance spectrum division. IIMI1 p,k and IIMI2 p,k They are the superposition of the amplitudes of the corresponding frequency components of the current responses in zones 2 and 3. As the degradation degree increases, IIMI1 p,k Reduced, IIMI2 p,k Increase.

[0063] As discussed above, the degree of degradation has a weakening effect on the monitoring indicators based on area 2. Therefore, IIMI1 p,k The change will be less than IIMI2 p,k , which means IIMI2 p,k It is more sensitive to the degradation of inter-turn insulation. Therefore, the inter-turn insulation monitoring index IIMI proposed in this paper p Based on IIMI2 p,k The obtained formula is as follows:

[0064]

[0065] Where m is the number of switching events. The switching frequency of the inverter is usually above several kHz, so a large number of transient current responses can be obtained within a few milliseconds. In equation (9), this averaging can effectively reduce the impact of noise and system uncertainty.

[0066] Since the switching frequency of the inverter is usually several kHz or above, there are a large number of switching events during the normal operation of the variable frequency motor system. Good monitoring accuracy can be obtained by simply averaging the characteristic parameters. The specific inter-turn insulation status evaluation process is as follows: Figure 1 During the operation of the motor, high-frequency voltage and current sensors are used to collect the three-phase voltage output of the inverter and the motor current, and the corresponding transient current responses are extracted according to the PWM voltage excitation of different phases. The inter-turn insulation state evaluation index IIMI2 of different phase windings is extracted by combining the boundary frequency of the impedance area division. A 、IIMI2 B 、IIMI2 C , to realize the insulation status evaluation of motor winding turns.

[0067] The PWM voltage excitation mode of the inverter directly affects the transient current response of the switch. Therefore, in order to ensure the validity of the monitoring results, it is necessary to determine the qualified PWM voltage excitation.

[0068] The high frequency characteristics of the PWM voltage depend mainly on its rise time. Figure 4 is the PWM voltage rise time (t r ) and the corresponding switching transient current response amplitude (I amp ) statistical chart, where t r is the time it takes for the PWM voltage to rise from 10% to 90% of the DC voltage. It can be seen that t r The smaller, I amp The larger the rise time, the higher the excitation voltage. In the positive half cycle of the load current, t r The minimum value, I ampMore importantly, they are almost constant, which is of great significance for the monitoring of winding insulation condition based on switching transient current.

[0069] In order to explain the above phenomenon in detail, the following studies were conducted: Figure 5 The shown one contains two IGBTs (S H and S L ) circuit diagram of a half-bridge inverter. The main parasitic components are the gate-emitter capacitance (C ge ), collector-gate capacitance (C cg ) and the collector-emitter capacitance (C ce ). The output current polarity is defined as positive when the current flows out of the midpoint (A) of the half-bridge. Figure 4 The detailed switching transitions when the output current is positive are shown. (a)-(c) represent the switching transitions from the upper switch S H To the lower switch S L The conduction phase changes, (c)-(d) represent the opposite situation.

[0070] Figure 5 The corresponding output voltage is Figure 6 As shown, V AN is the voltage between the DC link midpoint A and the negative point N. H When it is turned on, the load current flows through S H ,V AN +V DC At t1, for S H Apply a shutdown signal to S L The anti-parallel diode applies a reverse voltage. H Output capacitance (loss = C cg +C ce ) is charged, and S L Output capacitance (loss = C cg +C ce ) discharges, so V AN The fall time depends on the instantaneous value of the load current and the output capacitor loss, as shown in equation (10). L The output capacitor voltage V AN drops to 0V, and the current flows through S at t2 L The anti-parallel diode, such as Figure 5 (c) The current will flow directly from S L The anti-parallel diode transfers to S H , and V AN will immediately rise from 0V to +V DC In this case, V AN From 0V to +V DCThe rise time of the gate driver is determined only by the gate resistance (R g ) control. Since the voltage rises very quickly, the rising edge of VAN is recorded as a step edge, such as Figure 6 As shown at t3 in (a).

[0071]

[0072] When the load current is negative, the following can be obtained based on similar principles: Figure 6 (b) shows the switching transition, where the rising edge t r is the slope, the falling edge t f In summary, when the load current is positive, V AN The falling edge of V is affected by the load current and parasitic capacitance. Conversely, when the current is negative, V AN The rising edge is affected by the load current and parasitic capacitance.

[0073] Figure 7 The PWM voltage rise time (t r ) and fall time (t f ) statistics, where t f It is the time for the PWM voltage to drop from 90% to 10% of the DC voltage. When the current is positive, t r short, and is not affected by the load current; when the current is negative, t r When the positive current is greater than t r , and the greater the absolute value of the negative current, t r The smaller the t f The trend is opposite. Therefore, in order to ensure the consistency of PWM excitation characteristics, the rising edge of the PWM voltage under positive load current or the falling edge of the PWM voltage under negative load current can be selected as qualified PWM voltage excitation. This can minimize the impact of load current on the transient response of the switch.

[0074] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions. The sentence "includes an element defined by ... does not exclude the existence of other identical elements in the process, method, article or device including the element".

[0075] The above technical solutions only reflect the preferred technical solutions of the technical solutions of the present invention. Some changes that may be made to certain parts thereof by technicians in this technical field all reflect the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for monitoring inter-turn insulation degradation based on winding impedance spectrum division, characterized in that: include: Establish a high-frequency stator winding model and determine the sensitive areas of different impedance spectra for inter-turn insulation degradation; Establish analytical links between turn-to-turn insulation degradation and corresponding sensitive regions in winding impedance and switching transient current response spectra; The inter-turn insulation monitoring index is extracted based on the transient current response of impedance spectrum division to evaluate the inter-turn insulation status, and the evaluation results are verified using qualified PWM voltage excitation.

2. The method for monitoring turn-to-turn insulation degradation based on winding impedance spectrum division according to claim 1, characterized in that: In the high frequency stator winding model, C g1 and C g2 They are the equivalent capacitance between the winding end coil and the stator core, and between the neutral line and the stator core respectively; C g1 With C g2 The sum is the equivalent capacitance of the stator winding and the stator core at low frequency; C t is the capacitive coupling effect in the stator winding; R e is the loss equivalent resistance; R is the winding resistance; L d is the winding inductance.

3. The method for monitoring turn-to-turn insulation degradation based on winding impedance spectrum division according to claim 1, characterized in that: The process of determining the different impedance spectrum sensitive areas is as follows: Determine the impedance Z of single-phase winding to ground based on high-frequency stator winding model PG for: In the formula, Z PG Determined by the test frequency and model parameters, the inter-turn insulation capacitance C t Depending on the configuration, shape and material of the insulation system, the capacitance C t Will change, C t It increases with the increase of inter-turn insulation degradation; Z PG Amplitude vs. C t The partial derivative of is: in, Where K is always positive; Solving equation (2), we can obtain the positive and negative values ​​of partial derivatives in different frequency bands: In formula (5), the boundary frequencies f1 and f2 can be calculated according to (4)-(6) combined with the model parameters, and the different impedance spectrum sensitive areas are determined by dividing f1 and f2.

4. The method for monitoring turn-to-turn insulation degradation based on winding impedance spectrum division according to claim 1, characterized in that: The extraction process of the turn-to-turn insulation monitoring index is as follows: The spectrum of the transient current response is expressed as I(g), where g represents the discrete frequency order and the sampling rate F is used. s and the sample size N s Calculate the corresponding frequency f g , as shown below: The inter-turn insulation monitoring index in different impedance spectrum sensitive areas is defined as IIMI1 p,k and IIMI2 p,k Where, p is the p-phase winding, p=A,B,C; K is K th Switching event; f1 and f2 are the boundary frequencies of the above impedance spectrum division; Inter-turn insulation monitoring index IIMI p The expression is: where m is the number of switching events.

5. The method for monitoring turn-to-turn insulation degradation based on winding impedance spectrum division according to claim 1, characterized in that: The PWM voltage excitation selects a rising edge of the PWM voltage under a positive load current or a falling edge of the PWM voltage under a negative load current as a qualified PWM voltage excitation.

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