CN118091345A - Motor equivalent circuit, leakage current calculation method, insulation monitoring method and circuit - Google Patents

Abstract

The present invention relates to the technical field of motor insulation detection, and discloses a motor equivalent circuit, a leakage current calculation method, an insulation monitoring method and a circuit. The insulation monitoring method includes: clearing a DC signal within the dead time when the inverter switches the on-off state of its own target phase switch tube; after the inverter switches the on-off state of its own target phase switch tube, obtaining the leakage current on the AC side of the inverter; based on the calculation method of the motor leakage current parameter, obtaining a leakage current signal containing the frequency, period and amplitude of the leakage current; after attenuating, flipping and integrating the leakage current signal, obtaining a DC signal; and evaluating the insulation aging degree of the motor based on the voltage of the DC signal. The present invention can convert the leakage current signal of the motor into a DC signal with a slow attenuation speed, and detect the insulation aging degree of the motor according to the size of the DC signal, without relying on high precision and high current sampling rate, and the detection method is simple and the hardware cost is low.

Description

Motor equivalent circuit, leakage current calculation method, insulation monitoring method and circuit

Technical Field

The present invention relates to the technical field of motor insulation detection, and in particular to a motor equivalent circuit, a leakage current calculation method, and an insulation monitoring method and circuit.

Background technique

Motors have been widely used in electric vehicles, wind power generation, industrial production and other fields. Reliability is an important factor restricting their application in various fields. In industrial and transportation applications, sudden motor failures not only cause damage to the motor itself, but may also cause damage to the entire transmission system and even the power supply system. The impact of shutdowns and safety accidents caused by motor failures on the safety of life and property of personnel is immeasurable.

With the popularization of frequency conversion technology and the enhancement of the performance of power electronic switching devices, the electrical stress borne by the motor insulation system is much greater than that of the traditional motor insulation system; in addition, due to the demand for high energy density, the size of the motor has gradually become smaller, which further limits the heat dissipation capacity of the motor, resulting in a further increase in the failure rate of the motor insulation system.

The current traditional method mainly uses offline insulation testing, which mainly includes tests on insulation resistance, withstand voltage, impedance, impulse voltage, partial discharge, leakage current, etc. Traditional methods are used in motor factory testing, motor maintenance and other occasions, and cannot be used during motor operation. In order to avoid sudden failures of the motor during operation, a solution and system for online monitoring of the motor insulation status is proposed to improve the reliability of the motor during operation.

The existing insulation status monitoring technology mainly focuses on the online analysis of the insulation impedance spectrum, focusing on the insulation impedance of the baseband and mid-frequency band (within 1MHz). However, the insulation impedance of the low-frequency band reflects less insulation information and is less sensitive to insulation aging. Most of the existing insulation monitoring technologies are also highly dependent on hardware performance, requiring a large number of sampling high-precision measuring instruments, and also require high computing costs and long computing time.

Summary of the invention

Therefore, the technical problem to be solved by the present invention is to solve the problem that the motor winding equivalent circuit in the prior art cannot well reflect the aging of the motor insulation, thereby providing a motor equivalent circuit, a leakage current calculation method, an insulation monitoring method and a circuit.

In order to achieve the above object, the present invention provides the following technical solutions:

In a first aspect, the present invention provides a motor winding equivalent circuit, including: a first winding equivalent circuit and a second winding equivalent circuit, wherein the winding of the motor is divided into two parts, the first part is a first winding connected to a power supply end, and the second part is a remaining second winding; the first winding equivalent circuit, whose first end is connected to the power supply end, whose first end is the winding end of the motor, whose second end is connected to the first end of the second winding equivalent circuit, whose third end is connected to the second end of the second winding equivalent circuit and then grounded, the first winding equivalent circuit is an equivalent circuit of the power supply cable of the motor and the first winding; the second winding equivalent circuit is an equivalent circuit of the second winding.

The motor winding equivalent circuit provided by the present invention constructs a motor winding equivalent circuit model to provide a theoretical reference for insulation aging detection, and converts the parts prone to aging into the first winding equivalent circuit to facilitate subsequent calculation and analysis.

In an optional embodiment, the first winding equivalent circuit includes: a first equivalent resistor, a first equivalent inductor and a first equivalent capacitor, wherein the first equivalent resistor, whose first end is the winding end of the motor, and whose second end is connected to the first end of the first equivalent inductor, and the first equivalent resistor is the equivalent resistance of the power supply cable of the motor and the first part of the winding of the motor; the first equivalent inductor, whose second end is connected to the first end of the first equivalent capacitor and the first end of the second winding equivalent circuit, and the first equivalent inductor is the equivalent inductance of the power supply cable of the motor and the first part of the winding of the motor; the first equivalent capacitor, whose second end is connected to the second end of the second winding equivalent circuit and then grounded, and the first equivalent capacitor is the capacitance of the first part of the winding of the motor to ground.

In an optional embodiment, the second winding equivalent circuit includes: a second equivalent resistor, a second equivalent inductor, a second equivalent capacitor, a third equivalent resistor and a third equivalent capacitor, wherein the second equivalent resistor, a first end of which is connected to the first end of the third equivalent resistor, the first end of the third equivalent capacitor and the second end of the first equivalent inductor, and a second end of which is connected to the first end of the second equivalent inductor; the second end of the second equivalent inductor, a second end of which is connected to the second end of the third equivalent resistor, the second end of the third equivalent capacitor and the first end of the second equivalent capacitor; the second end of the second equivalent capacitor, a second end of which is connected to the second end of the first equivalent capacitor and then grounded.

In a second aspect, the present invention provides a method for calculating motor leakage current parameters, which is calculated based on the motor winding equivalent circuit of the first aspect. The method for calculating motor leakage current parameters includes: obtaining the leakage current in the first winding equivalent circuit; calculating the frequency of the leakage current based on the resonant frequency of the leakage current in the first winding equivalent circuit; and calculating the period and amplitude of the leakage current based on the parameters of the first winding equivalent circuit and the second winding equivalent circuit.

The method for calculating the motor leakage current parameters provided by the present invention can accurately analyze and calculate the characteristic parameters such as frequency and amplitude of the leakage current at the aging part, obtain the changing trend of each characteristic parameter with the aging degree of the motor, and thus obtain and predict the aging degree of the motor.

In an optional implementation, the calculation formula for the frequency of the leakage current is:

Wherein, f _HF is the frequency of the leakage current; L ₁ is the first equivalent inductance; and C _g1 is the first equivalent capacitance.

In an optional implementation, the calculation formula for the leakage current period is:

Wherein, _t0 is the period of the leakage current; _L1 is the first equivalent inductance; _Cg1 is the first equivalent capacitance; _Cg2 is the second equivalent capacitance; _Rp is the third equivalent resistance; the calculation formula of the leakage current amplitude is:

Where _A0 is the amplitude of the leakage current.

In the third aspect, the present invention provides a method for monitoring motor insulation aging, wherein the power supply end of the motor is connected to the AC side of the inverter, and the method comprises: clearing the DC signal within the dead time when the inverter switches the on-off state of its own target phase switch tube; after the inverter switches the on-off state of its own target phase switch tube, obtaining the leakage current on the AC side of the inverter; based on the calculation method of the motor leakage current parameters of the second aspect, obtaining a leakage current signal including the frequency, period and amplitude of the leakage current; obtaining a DC signal after attenuating, flipping and integrating the leakage current signal; and evaluating the degree of insulation aging of the motor based on the voltage of the DC signal.

The motor insulation aging detection method provided by the present invention obtains a DC signal by successively attenuating, flipping and integrating the leakage current signal of the motor. The DC signal decays slowly, and the above-mentioned processing process does not change or eliminate the characteristic information of the leakage current. It is convenient to collect and process under the condition of retaining the characteristic information of the leakage current. The detection result does not depend on the accuracy of the instrument and the current sampling rate, which improves the problem of high current sampling rate required by the traditional monitoring method. The integral zeroing circuit resets and clears the output end of the integration circuit before the integration circuit outputs the DC signal each time, so as to avoid ensuring that the DC signal is affected by the DC signal during the last insulation aging detection, and the signal processing speed is fast and the monitoring result is accurate. The leakage current signal is processed by the hardware circuit, which reduces the calculation cost of the software, and the signal sampling can be directly performed in the motor controller without adding an additional microcontroller. Since different insulation aging degrees will lead to different leakage current voltages, and the magnitude of the DC signal voltage with a slow decay speed is easy to collect and detect, the insulation aging degree of the motor can be quickly evaluated by the magnitude of the DC signal voltage.

In a fourth aspect, the present invention provides an insulation aging monitoring circuit for implementing the monitoring method of the third aspect, the circuit comprising: a current sensor, a signal attenuation circuit, a multiplier, an integration circuit, an integration clearing circuit and a controller, wherein the current sensor is connected to the power supply end of the motor in a non-contact manner, and its output end is connected to the input end of the signal attenuation circuit, and is used to collect the common-mode current of the motor and then output a leakage current signal; the signal attenuation circuit, whose input end is connected to the power supply end of the motor, whose input end receives the leakage current signal of the motor, and whose output end is connected to the input end of the multiplier, and is used to attenuate the leakage current signal to within a preset voltage range and then output a first-level signal; the multiplier, whose output end is connected to the input end of the integration circuit, and is used to collect the common-mode current of the motor and then output a leakage current signal; After flipping the negative half-cycle signal of the first-stage signal to the positive half-cycle, a second-stage signal is output; an integration circuit, whose output end is connected to the input end of the controller, and is used to integrate the second-stage signal and output a DC signal; a controller, whose first output end is connected to the control end of the inverter, and is used to control the inverter to switch the on-off state of the target phase switch tube, output a reset signal within the dead time of the inverter switching the on-off state of the target phase switch tube, and evaluate the insulation aging degree of the motor based on the voltage of the DC signal; an integration reset circuit, whose input end is connected to the second output end of the controller, whose input end receives the reset signal, and whose output end is connected to the output end of the integration circuit, and is used to reset the DC signal output by the integration circuit based on the reset signal.

The insulation aging detection circuit provided by the present invention sequentially attenuates, flips and integrates the leakage current signal of the device to be detected to obtain a DC signal. The DC signal decays slowly, and the above-mentioned processing will not change or eliminate the characteristic information of the leakage current. It is convenient to collect and process under the condition of retaining the characteristic information of the leakage current. The detection result does not depend on the accuracy of the instrument and the current sampling rate, which improves the problem of high current sampling rate required by traditional monitoring methods, and only needs to attenuate, flip and integrate the leakage current signal to generate the aging detection result. The integral zeroing circuit resets the output end of the integration circuit to zero before the integration circuit outputs the DC signal each time, so as to avoid the DC signal being affected by the DC signal during the last insulation aging detection. The signal processing speed is fast, the processing process is simple, and the detection result is accurate. Since different degrees of insulation aging will lead to different voltages of the leakage current, and the magnitude of the DC signal voltage with a slow decay speed is easy to collect and detect, the degree of insulation aging of the device to be detected can be quickly evaluated by the magnitude of the DC signal voltage.

In an optional embodiment, the signal attenuation circuit includes: a first resistor, a second resistor, a third resistor, a fourth resistor and a first operational amplifier, wherein the first resistor has a first end for inputting a leakage current signal, and a second end for connecting to a first end of the second resistor and an inverting input of the first operational amplifier; the second resistor has a second end for connecting to a non-inverting output of the first operational amplifier and an input of a multiplier; the third resistor has a first end for connecting to ground, and a second end for connecting to a first end of the fourth resistor and the non-inverting input of the first operational amplifier; and the fourth resistor has a second end for connecting to an inverting output of the first operational amplifier and an input of the multiplier.

In the insulation aging detection circuit provided by the present invention, the signal attenuation circuit outputs an attenuated first-level signal with an amplitude within a preset voltage range according to the voltage difference between two signals at the input end, so as to meet the voltage requirement of the subsequent hardware.

In an optional embodiment, the integration circuit includes: a fifth resistor, a sixth resistor, a seventh resistor, a first capacitor and a second operational amplifier, wherein the fifth resistor has a first end connected to the output of the multiplier, and a second end connected to the inverting input of the second operational amplifier, the first end of the sixth resistor and the first end of the first capacitor; the sixth resistor has a second end connected to the second end of the first capacitor, the output of the second operational amplifier and the output of the integral clearing circuit; the seventh resistor has a first end connected to the ground, and a second end connected to the non-inverting input of the second operational amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a structural diagram of a specific circuit of a motor winding equivalent circuit according to an embodiment of the present invention;

FIG2 is a flow chart of a method for calculating a motor leakage current parameter according to an embodiment of the present invention;

FIG3 is a common mode voltage and current curve diagram of a motor according to an embodiment of the present invention;

FIG4 is an impedance spectrum diagram according to an embodiment of the present invention;

FIG5 is a schematic flow chart of a method for monitoring motor insulation aging according to an embodiment of the present invention;

6 is a composition diagram of a specific example of an insulation aging monitoring circuit according to an embodiment of the present invention;

7 is a control timing diagram of an insulation aging monitoring circuit according to an embodiment of the present invention;

FIG. 8 is a structural diagram of a specific circuit of the insulation aging monitoring circuit according to an embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

The present embodiment provides a motor winding equivalent circuit, including: a first winding equivalent circuit 1 and a second winding equivalent circuit 2, wherein the winding of the motor is divided into two parts, the first part is a first winding connected to a power supply end, and the second part is a remaining second winding; the first winding equivalent circuit 1, whose first end is connected to the power supply end, whose first end is the winding end of the motor, whose second end is connected to a first end of the second winding equivalent circuit 2, whose third end is connected to a second end of the second winding equivalent circuit 2 and then grounded, the first winding equivalent circuit 1 is an equivalent circuit of the power supply cable and the first winding of the motor; the second winding equivalent circuit 2 is an equivalent circuit of the second winding.

Specifically, as shown in Figure 1, the first winding equivalent circuit 1 includes: a first equivalent resistor _R9 , a first equivalent inductor _L1 and a first equivalent capacitor _Cg1 , wherein the first equivalent resistor _R9 , a first end thereof is the winding end W of the motor, and a second end thereof is connected to the first end of the first equivalent inductor _L1 , and the first equivalent resistor _R9 is the equivalent resistance of the power supply cable of the motor and the first part of the winding of the motor; the first equivalent inductor _L1 , a second end thereof is connected to the first end of the first equivalent capacitor _Cg1 and the first end of the second winding equivalent circuit 2, and the first equivalent inductor _L1 is the equivalent inductance of the power supply cable of the motor and the first part of the winding of the motor; the first equivalent capacitor _Cg1 , a second end thereof is connected to the second end of the second winding equivalent circuit 2 and then grounded, and the first equivalent capacitor is the capacitance of the first part of the winding of the motor to ground.

Specifically, as shown in Figure 1, the second winding equivalent circuit 2 includes: a second equivalent resistor _R10 , a second equivalent inductor _L2 , a second equivalent capacitor _Cg2 , a third equivalent resistor _Rp and a third equivalent capacitor _Cp , wherein the second equivalent resistor _R10 , a first end thereof is connected to the first end of the third equivalent resistor _Rp , the first end of the third equivalent capacitor _Cp and the second end of the first equivalent inductor _L1 , and a second end thereof is connected to the first end of the second equivalent inductor _L2 ; the second end thereof is connected to the second end of the third equivalent resistor _Rp , the second end of _the third equivalent capacitor _Cp and the first end of the second equivalent capacitor _Cg2 ; the second end thereof is connected to the second end of _{the first equivalent capacitor Cg1 and} then grounded.

For example, in FIG1 , W is the motor winding end, G is the ground (or housing), and the common mode voltage at the winding end is generally the largest, and the electrical stress is the largest. Therefore, the winding end is the part of the entire motor winding where the insulation aging to the ground is the most serious. Therefore, by analyzing the leakage current flowing through the winding end, the motor leakage current can be obtained, thereby evaluating the degree of insulation aging of the motor.

The motor winding equivalent circuit provided in this embodiment constructs a motor winding equivalent circuit model to provide a theoretical reference for insulation aging detection, and converts the parts prone to aging into the first winding equivalent circuit to facilitate subsequent calculation and analysis.

This embodiment provides a method for calculating the motor leakage current parameter, which is calculated based on the motor winding equivalent circuit of the above embodiment. As shown in FIG2 , the method for calculating the motor leakage current parameter includes:

Step S1: Obtain the leakage current in the first winding equivalent circuit.

Exemplarily, referring to FIG1 , since the first equivalent capacitor C _g1 represents the equivalent capacitance to the ground near the line end, the parameters of the first equivalent resistor R ₉ , the first equivalent inductor L ₁ , and the first equivalent capacitor C _g1 are much smaller than the second equivalent resistor R ₁₀ , the second equivalent inductor L ₂ , and the second equivalent capacitor C _g2 , the high-frequency current generated by the switch at the power supply end of the motor generally flows to the ground through the first equivalent capacitor C _g1 . Therefore, it can be considered that the high-frequency leakage current in the first winding equivalent circuit is sensitive to insulation aging changes.

Step S2: Calculate the frequency of the leakage current according to the resonant frequency of the leakage current in the first winding equivalent circuit.

It should be noted that in Figure 1, in an actual motor, the first equivalent capacitance C _g1 in the equivalent model is much smaller than the second equivalent capacitance C _g2 , the first equivalent inductance L ₁ is much smaller than the second equivalent inductance L ₂ , the first equivalent resistance R ₉ is much smaller than the second equivalent resistance R ₁₀ , and at high frequencies, the inductance of the resistor in the circuit has a much greater impact on the motor impedance than the resistance. Combined with the actual motor parameters, the small-magnitude terms in the formula are simplified and omitted to obtain the following entire calculation formula.

Exemplarily, referring to FIG1 , after obtaining the high-frequency leakage current in the first winding equivalent circuit, the frequency f _HF of the leakage current is:

Step S3: Calculate the period and amplitude of the leakage current based on the parameters of the second winding equivalent circuit.

For example, the common mode voltage form of the motor is shown in Figure 3. The waveform motor in the frame is the common mode voltage form before and after the IGBT of any phase is turned on. The amplitude A of the voltage waveform is 1/3 times the bus voltage U _dc . The voltage waveform u(t) at the moment of IGBT turn-on is defined as a ramp plus a platform form, where τ represents the voltage rise time. Then u(t) is expressed as follows:

After Laplace transformation of u(t), we get U(s) as follows:

The high frequency current response I _HF (s) can be expressed as follows:

Where Z _CM (s) is the high frequency impedance, calculated as:

Then the waveform of the high-frequency current response i _HF is:

Among them, the phase parameters p ₁ ~ p ₃ are:

Among them, the parameter a is:

Wherein, the angular velocity ω is:

The parameters of the equivalent model determine the parameters of the leakage current, such as the relationship between the leakage current period _t0 and the amplitude _A0 and the components in the model. When the insulation ages, _Cg1 decreases, which will lead to a decrease in _t0 and _A0. The specific relationship is as follows:

Exemplarily, the parameters of the motor model are extracted based on the equivalent circuit shown in FIG1 and an actual motor, and the obtained data are shown in Table 1. At this time, the calculated values of the common-mode impedance spectrum of the actual motor and the impedance spectrum of the equivalent circuit are shown in FIG4. It can be seen that the two have a good degree of overlap, and the equivalent model can better simulate the two common-mode resonance point valleys of the actual motor. The two resonance points are named MFTR and HFTR, respectively, where HFTR is the frequency and impedance corresponding to the leakage current generated by the switch.

Table 1

resistance resistance inductance Inductance capacitance Capacitance R9 1(mΩ) L1 1.4(uH) Cg1 1.1(nF) R10 10(mΩ) L2 30(uH) Cg2 11.9(nF) R 80(Ω) Cp 0.1(nF)

The method for calculating the motor leakage current parameters provided by the present invention can accurately analyze and calculate the characteristic parameters such as frequency and amplitude of the leakage current at the aging part, obtain the changing trend of each characteristic parameter with the aging degree of the motor, and thus obtain and predict the aging degree of the motor.

This embodiment provides a method for monitoring motor insulation aging. As shown in FIG5 , the power supply end of the motor is connected to the AC side of the inverter. The method includes:

Step S4: clearing the DC signal within the dead time when the inverter switches the on/off state of its own target phase switch.

Step S5: After the inverter switches the on/off state of its own target phase switch tube, the leakage current on the AC side of the inverter is obtained.

Step S6: Based on the calculation method of the motor leakage current parameters of the above embodiment and any optional implementation manner thereof, a leakage current signal including the frequency, period and amplitude of the leakage current is obtained.

Step S7: After attenuation, inversion and integration processing of the leakage current signal, a DC signal is obtained.

Step S8: Evaluate the insulation aging degree of the motor based on the voltage of the DC signal.

Exemplarily, the inverter switches the switch state of the upper and lower tubes of the target phase, thereby switching the power supply state to the motor. Take the case where the lower tube of the target phase of the inverter is turned off and the upper tube is turned on as an example: leakage current will be generated on the AC side of the inverter at the moment the upper tube is turned on. When the lower tube of the target phase is turned off, the DC signal output by the last insulation aging monitoring is cleared, and the motor winding equivalent circuit is used in combination with the above-mentioned motor leakage current parameter calculation method to obtain the leakage current signal containing the frequency, period and amplitude of the leakage current. The leakage current signal is then attenuated, flipped, and integrated in sequence. After the original leakage current waveform is completely attenuated to 0, a DC signal with a slower decay speed is obtained, and the DC signal is sampled. The size of the DC signal reflects the degree of aging of the motor insulation. Generally, the DC signal is sampled multiple times and the average value is calculated, and the insulation aging degree of the motor is evaluated according to the size of the calculation result.

It should be noted that after sampling, data screening is performed and sampling results that meet the following conditions can be retained as the basis for status assessment:

(1) During the switching operation of the inverter target phase for insulation status monitoring, there is no switching operation of other phases.

(2) The target phase turn-on time is not less than the time it takes for the original leakage current to decay to 0.

(3) The phase current of the target phase at the sampling time is greater than 0.

It should be noted that the motor includes but is not limited to a single-phase motor, an open-winding motor and a multi-phase motor.

The motor insulation aging detection method provided in this embodiment obtains a DC signal by successively attenuating, flipping and integrating the leakage current signal of the motor. The DC signal decays slowly, and the above-mentioned processing process will not change or eliminate the characteristic information of the leakage current. It is convenient to collect and process under the condition of retaining the characteristic information of the leakage current. The detection result does not depend on the accuracy of the instrument and the current sampling rate, which improves the problem of high current sampling rate required by the traditional monitoring method. And the integral zeroing circuit resets the output end of the integration circuit to zero before the integration circuit outputs the DC signal each time, so as to avoid ensuring that the DC signal is affected by the DC signal during the last insulation aging detection, and the signal processing speed is fast and the monitoring result is accurate. The leakage current signal is processed by the hardware circuit, which reduces the calculation cost of the software, and the signal sampling can be directly performed in the motor controller without adding an additional microcontroller. Since different insulation aging degrees will lead to different leakage current voltages, and the magnitude of the DC signal voltage with a slow decay speed is easy to collect and detect, the degree of insulation aging of the motor can be quickly evaluated by the magnitude of the DC signal voltage.

This embodiment provides an insulation aging monitoring circuit for implementing the monitoring method of the above embodiment. As shown in FIG. 6 , the circuit includes: a signal attenuation circuit 31 , a multiplier 32 , an integration circuit 33 , an integration clearing circuit 34 , a controller 35 and a current sensor 36 .

As shown in FIG6 , the current sensor 36 is connected to the power supply end of the motor in a contactless manner, and its output end is connected to the input end of the signal attenuation circuit 31 , and is used to collect the common mode current of the motor and then output a leakage current signal.

As shown in FIG6 , the signal attenuation circuit 31 has its output end connected to the input end of the multiplier 32 , and is used to output a first level signal after attenuating the leakage current signal to within a preset voltage range.

As shown in FIG6 , the multiplier 32 has its output end connected to the input end of the integration circuit 33 , which is used to flip the negative half-cycle signal of the first-stage signal to the positive half-cycle and then output the second-stage signal.

As shown in FIG6 , the output end of the integration circuit 33 is connected to the input end of the controller 35 , and is used to integrate the second-stage signal and output a DC signal Uo.

As shown in Figure 6, the controller 35, whose first output end is connected to the control end of the inverter, is used to control the on-off state of the inverter switching target phase switch tube, output a reset signal within the dead time of the inverter switching the on-off state of the target phase switch tube, and evaluate the insulation aging degree of the motor based on the voltage of the DC signal Uo.

As shown in FIG6 , the integral reset circuit 34 has its input end connected to the second output end of the controller 35 , its input end receives a reset signal, and its output end is connected to the output end of the integral circuit 33 , and is used to reset the DC signal output by the integral circuit based on the reset signal.

Exemplarily, referring to FIG6 and FIG7, taking the case where the controller 35 controls the lower tube of the target phase of the inverter to be turned off and the upper tube to be turned on as an example, at the moment when the lower tube is turned off and during the dead time when the upper tube is not turned on, the controller 35 sends a reset signal to the integral reset circuit 34, so that the integral reset circuit 34 resets the output voltage of the integral circuit 33 based on the reset signal. At this time, the leakage current signal of the motor is a decaying sinusoidal signal.

For example, in Fig. 6, the power supply cables of each phase winding of the motor pass through the current sensor 36. During normal operation, the magnetic field of each phase load current is offset, and only the common mode current of the motor is measured by the current sensor 36. The current sensor 36 outputs a leakage current signal to the signal attenuation circuit 31 based on the collected common mode current.

Exemplarily, referring to FIG6 and FIG7, when the signal attenuation circuit 31 collects the leakage current signal, the leakage current signal includes characteristic information such as the frequency, period, and amplitude of the leakage current. The signal attenuation circuit 31 attenuates the leakage current signal to a preset voltage range to meet the voltage requirements of the subsequent circuit and avoid excessive voltage amplitude from damaging the hardware of the subsequent circuit. The multiplier 32 flips the negative half-cycle of the first-stage signal output by the signal attenuation circuit 31 to the positive half-cycle and then outputs the second-stage signal. The integration circuit 33 integrates the second-stage signal to convert the second-stage signal into a DC signal Uo with a slow attenuation speed and smoothness. The controller 35 evaluates the insulation aging degree of the motor by comparing the output DC signal Uo with the parameters of the motor when it leaves the factory.

For example, in FIG. 6 , the controller 35 can also perform data transmission with a terminal such as a computer PC, and a user can send a control instruction to the controller 35 through the computer PC, or receive the insulation aging degree monitoring result of the motor returned by the controller 35 .

The insulation aging detection circuit provided by the present invention sequentially attenuates, flips and integrates the leakage current signal of the device to be detected to obtain a DC signal. The DC signal decays slowly, and the above-mentioned processing will not change or eliminate the characteristic information of the leakage current. It is convenient to collect and process under the condition of retaining the characteristic information of the leakage current. The detection result does not depend on the accuracy of the instrument and the current sampling rate, which improves the problem of high current sampling rate required by traditional monitoring methods, and only needs to attenuate, flip and integrate the leakage current signal to generate the aging detection result. The integral zeroing circuit resets the output end of the integration circuit to zero before the integration circuit outputs the DC signal each time, so as to avoid the DC signal being affected by the DC signal during the last insulation aging detection. The signal processing speed is fast, the processing process is simple, and the detection result is accurate. Since different degrees of insulation aging will lead to different voltages of the leakage current, and the magnitude of the DC signal voltage with a slow decay speed is easy to collect and detect, the degree of insulation aging of the device to be detected can be quickly evaluated by the magnitude of the DC signal voltage.

In some optional embodiments, as shown in FIG8 , the signal attenuation circuit 31 includes: a first resistor R ₁ , a second resistor R ₂ , a third resistor R ₃ , a fourth resistor R ₄ and a first operational amplifier U ₁ , wherein the first resistor R ₁ has a first end to which the leakage current signal is input, and a second end thereof is connected to a first end of the second resistor R ₂ and an inverting input end of the first operational amplifier U ₁ ; the second resistor R ₂ has a second end connected to a non-inverting output end of the first operational amplifier U ₁ and an input end of the multiplier 32 ; the third resistor R ₃ has a first end connected to ground, and a second end thereof is connected to a first end of the fourth resistor R ₄ and the non-inverting input end of the first operational amplifier U ₁ ; the fourth resistor R ₄ has a second end connected to an inverting output end of the first operational amplifier U ₁ and an input end of the multiplier 32 .

As shown in FIG8 , the integration circuit 33 includes: a fifth resistor R ₅ , a sixth resistor R ₆ , a seventh resistor R ₇ , a first capacitor C ₁ and a second operational amplifier U ₂ , wherein the fifth resistor R ₅ has a first end connected to the output end of the multiplier 32 , and a second end connected to the inverting input end of the second operational amplifier U ₂ , a first end of the sixth resistor R ₆ and a first end of the first capacitor C ₁ ; the sixth resistor R ₆ has a second end connected to the second end of the first capacitor C ₁ and the output end of the second operational amplifier U ₂ ; the seventh resistor R ₇ has a first end connected to the ground, and a second end connected to the non-inverting input end of the second operational amplifier U ₂ .

Exemplarily, in FIG8 , the integral clearing circuit 34 includes: the inverting input terminal of the third operational amplifier U ₃ is connected to its output terminal and the output terminal of the second operational amplifier U ₂ , its enable terminal receives the clearing signal, and its non-inverting input terminal is grounded. When the controller 35 sends a clearing signal, the third operational amplifier U ₃ outputs a 0V voltage, thereby clearing the DC signal Uo at the output terminal of the second operational amplifier U ₂ .

Specifically, in FIG8 , the leakage current signal is a sine wave signal with a fast decay speed. The leakage current signal is input to the inverting input terminal of the first operational amplifier U ₁ through the first resistor R _1. The non-inverting input terminal of the first operational amplifier U ₁ is grounded through the third resistor R _3. The first operational amplifier U ₁ attenuates the signal difference between the non-inverting input terminal and the reverse input terminal and then outputs the first-level signal. The multiplier 32 squares the first-level signal, flips the negative half-cycle part of the first-level signal to the positive half-cycle, and then performs integration processing through the integration circuit 33, and outputs a DC signal Uo with a slow decay speed.

Specifically, in FIG8 , at the beginning of each insulation aging detection, the integral clearing circuit 34 collects a clearing signal. When the clearing signal is at a high level, the third operational amplifier _U3 outputs a 0V voltage, thereby clearing the DC signal Uo at the output end of the second operational amplifier _U2 , and clearing the result of the last insulation aging monitoring output.

It should be noted that, referring to FIG. 1 and FIG. 8 , the relationship between the output value U _O of the integration circuit 33 and the parameters of the equivalent circuit under an ideal state is as follows. When the insulation ages, the decrease of C _g1 will lead to the decrease of U _O , that is:

For example, when the insulation state of the equipment to be tested is completely healthy, the voltage of the output signal after measurement is generally equal to the voltage recorded when leaving the factory; as the equipment to be tested ages, the voltage of the output signal will gradually decrease. When the voltage of the output signal drops to 70% of the original recorded voltage, it is determined that the insulation is severely aged, or there is a potential risk of failure.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims (10)

1. A motor winding equivalent circuit, characterized in that it comprises: a first winding equivalent circuit and a second winding equivalent circuit, wherein: The winding of the motor is divided into two parts, the first part is a first winding connected to the power supply end, and the second part is a remaining second winding; A first winding equivalent circuit, wherein the first end is connected to the power supply end, the first end is the winding end of the motor, the second end is connected to the first end of the second winding equivalent circuit, the third end is connected to the second end of the second winding equivalent circuit and then grounded, and the first winding equivalent circuit is the power supply cable of the motor and the equivalent circuit of the first winding; The second winding equivalent circuit is an equivalent circuit of the second winding. 2. The motor winding equivalent circuit according to claim 1, characterized in that the first winding equivalent circuit comprises: a first equivalent resistance, a first equivalent inductance and a first equivalent capacitance, wherein: A first equivalent resistor, a first end of which is a winding end of the motor, and a second end of which is connected to the first end of the first equivalent inductor, the first equivalent resistor being an equivalent resistance of a power supply cable of the motor and a first part of the winding of the motor; A first equivalent inductor, a second end of which is connected to a first end of the first equivalent capacitor and a first end of the second winding equivalent circuit, wherein the first equivalent inductor is an equivalent inductance of a power supply cable of the motor and a first part of the winding of the motor; A first equivalent capacitor has a second end connected to a second end of the second winding equivalent circuit and then grounded. The first equivalent capacitor is the capacitance to ground of the first part of the winding of the motor. 3. The motor winding equivalent circuit according to claim 2, characterized in that the second winding equivalent circuit comprises: a second equivalent resistor, a second equivalent inductor, a second equivalent capacitor, a third equivalent resistor and a third equivalent capacitor, wherein: a second equivalent resistor, a first end of which is connected to the first end of the third equivalent resistor, the first end of the third equivalent capacitor, and the second end of the first equivalent inductor, and a second end of which is connected to the first end of the second equivalent inductor; A second equivalent inductor, a second end of which is connected to the second end of the third equivalent resistor, the second end of the third equivalent capacitor, and the first end of the second equivalent capacitor; A second equivalent capacitor, a second end of which is connected to the second end of the first equivalent capacitor and then grounded. 4. A method for calculating a motor leakage current parameter, characterized in that the calculation is performed based on the motor winding equivalent circuit according to claim 3, and the method for calculating the motor leakage current parameter comprises: obtaining a leakage current in an equivalent circuit of the first winding; Calculating the frequency of the leakage current according to the resonant frequency of the leakage current in the first winding equivalent circuit; The period and amplitude of the leakage current are calculated based on the parameters of the first winding equivalent circuit and the second winding equivalent circuit. 5. The method for calculating the motor leakage current parameter according to claim 4, characterized in that: The calculation formula of the frequency of the leakage current is: Wherein, f _HF is the frequency of the leakage current; L ₁ is the first equivalent inductance; and C _g1 is the first equivalent capacitance. 6. The method for calculating the motor leakage current parameter according to claim 5, characterized in that: The calculation formula of the leakage current period is: Wherein, _t0 is the period of the leakage current; _L1 is the first equivalent inductance; _Cg1 is the first equivalent capacitance; _Cg2 is the second equivalent capacitance; _Rp is the third equivalent resistance; The calculation formula for the amplitude of the leakage current is: Where _A0 is the amplitude of the leakage current. 7. A method for monitoring motor insulation aging, characterized in that the power supply end of the motor is connected to the AC side of the inverter, and the method comprises: The DC signal is cleared within the dead time when the inverter switches the on/off state of its own target phase switch tube; When the inverter switches the on/off state of its own target phase switch tube, the leakage current on the AC side of the inverter is obtained; Based on the calculation method of the motor leakage current parameter according to any one of claims 4 to 6, a leakage current signal including the frequency, period and amplitude of the leakage current is obtained; After attenuation, inversion and integration processing are performed on the leakage current signal, a direct current signal is obtained; The insulation aging degree of the motor is evaluated based on the voltage of the DC signal. 8. An insulation aging monitoring circuit, characterized in that it is used to implement the monitoring method according to claim 7, the circuit comprises: a current sensor, a signal attenuation circuit, a multiplier, an integration circuit, an integration clearing circuit and a controller, wherein: A current sensor, which is connected to the power supply end of the motor in a non-contact manner, and whose output end is connected to the input end of the signal attenuation circuit, and is used to collect the common mode current of the motor and then output a leakage current signal; A signal attenuation circuit, whose output end is connected to the input end of the multiplier, and is used to output a first level signal after attenuating the leakage current signal to within a preset voltage range; a multiplier, whose output end is connected to the input end of the integration circuit, and which is used to flip the negative half-cycle signal of the first-stage signal to the positive half-cycle and then output a second-stage signal; an integrating circuit, whose output terminal is connected to the input terminal of the controller, and is used to integrate the second-stage signal and output a DC signal; A controller, whose first output terminal is connected to the control terminal of the inverter, and is used to control the inverter to switch the on-off state of the target phase switch tube, output a reset signal within the dead time of the inverter switching the on-off state of the target phase switch tube, and evaluate the insulation aging degree of the motor based on the voltage of the DC signal; An integral zeroing circuit, whose input end is connected to the second output end of the controller, whose input end receives a zeroing signal, and whose output end is connected to the output end of the integral circuit, is used to zero the DC signal output by the integral circuit based on the zeroing signal. 9. The insulation aging monitoring circuit according to claim 8, characterized in that the signal attenuation circuit comprises: a first resistor, a second resistor, a third resistor, a fourth resistor and a first operational amplifier, wherein: a first resistor, a first end of which is input with the leakage current signal, and a second end of which is connected with the first end of the second resistor and the inverting input end of the first operational amplifier; a second resistor, a second end of which is connected to the in-phase output end of the first operational amplifier and the input end of the multiplier; a third resistor, a first end of which is grounded, and a second end of which is connected to the first end of the fourth resistor and the non-inverting input end of the first operational amplifier; A fourth resistor has a second end connected to the inverting output end of the first operational amplifier and the input end of the multiplier. 10. The insulation aging monitoring circuit according to claim 8, characterized in that the integration circuit comprises: a fifth resistor, a sixth resistor, a seventh resistor, a first capacitor and a second operational amplifier, wherein: a fifth resistor, a first end of which is connected to the output end of the multiplier, and a second end of which is connected to the inverting input end of the second operational amplifier, the first end of the sixth resistor, and the first end of the first capacitor; a sixth resistor, a second end of which is connected to the second end of the first capacitor, the output end of the second operational amplifier, and the output end of the integral clearing circuit; A seventh resistor has a first end connected to the ground, and a second end connected to the non-inverting input terminal of the second operational amplifier.