CN118091345A - Motor equivalent circuit, leakage current calculation method, insulation monitoring method and circuit - Google Patents
Motor equivalent circuit, leakage current calculation method, insulation monitoring method and circuit Download PDFInfo
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- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
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Abstract
The 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, wherein the insulation monitoring method comprises the following steps: clearing the direct current signal in dead time of the inverter switching the on-off state of the target phase switching tube; after the inverter switches the on-off state of the target phase switching tube, acquiring leakage current of the alternating current side of the inverter; obtaining a frequency, period and amplitude leakage current signal containing leakage current based on a calculation method of a motor leakage current parameter; the leakage current signal is attenuated, overturned and integrated to obtain a direct current signal; and evaluating the insulation aging degree of the motor based on the voltage of the direct current signal. The invention can convert the leakage current signal of the motor into the direct current signal with slow attenuation speed, and detect the insulation aging degree of the motor according to the size of the direct current signal, without depending on high precision and high current sampling rate, and has simple detection method and low hardware cost.
Description
Technical Field
The invention relates to the technical field of motor insulation detection, in particular to a motor equivalent circuit, a leakage current calculation method, an insulation monitoring method and a circuit.
Background
The motor has been widely used in the fields of electric automobiles, wind power generation, industrial production and the like, and the reliability problem is an important factor restricting the application of the motor in various fields. In industrial, traffic and other applications, sudden motor faults not only cause damage to the motor, but also can damage the whole transmission system and even the power supply system, and the shutdown caused by the motor faults and the influence of safety accidents on the life and property safety of personnel are immeasurable.
With the popularization of frequency conversion technology and the enhancement of the performance of power electronic switching devices, the electric stress born by a motor insulation system is far greater than that of a traditional motor insulation system; in addition, for the requirement of high energy density, the volume of the motor is gradually reduced, so that the heat dissipation capacity of the motor is further limited, and the failure rate of the motor insulation system is further increased.
The traditional method mainly adopts off-line insulation test, and mainly comprises insulation resistance, voltage resistance, impedance, impulse voltage, partial discharge, leakage current and other tests. The traditional method is applied to occasions such as motor delivery test and motor maintenance, cannot be applied to the motor operation process, and in order to avoid sudden faults of the motor during operation, a scheme and a system for on-line monitoring of the insulation state of the motor are provided, so that the reliability of the motor in operation is improved.
The existing insulation state monitoring technology mainly adopts on-line analysis of insulation impedance frequency spectrums, focuses on insulation impedance of fundamental frequency and medium frequency bands (within 1 MHz), but insulation information reflected by insulation impedance of low frequency bands is less, and sensitivity to insulation aging is poor. Most of the existing insulation monitoring technologies also highly depend on hardware performance, require a large number of sampling high-precision measuring instruments, and also require higher calculation cost and longer calculation time.
Disclosure of Invention
Therefore, the invention aims to solve the technical problem that the motor winding equivalent circuit in the prior art cannot well reflect insulation aging of a motor, thereby providing the motor equivalent circuit, a leakage current calculation method, an insulation monitoring method and a circuit.
In order to achieve the above purpose, the present invention provides the following technical solutions:
In a first aspect, the present invention provides a motor winding equivalent circuit comprising: the motor comprises a first winding equivalent circuit and a second winding equivalent circuit, wherein the winding component of the motor is divided into two parts, the first part is a first winding connected with a power supply end, and the second part is a residual second winding; the first end of the first winding equivalent circuit is connected with the power supply end, the first end of the first winding equivalent circuit is a winding end of the motor, the second end of the first winding equivalent circuit is connected with the first end of the second winding equivalent circuit, the third end of the first winding equivalent circuit is connected with the second end of the second winding equivalent circuit and then grounded, and the first winding equivalent circuit is an equivalent circuit of a power supply cable of the motor and the first winding; the second winding equivalent circuit is an equivalent circuit of the second winding.
In order to provide theoretical reference for insulation aging detection, the motor winding equivalent circuit provided by the invention constructs a motor winding equivalent circuit model, and the parts easy to age are equivalent to a first winding equivalent circuit, so that the follow-up calculation and analysis are convenient.
In an alternative embodiment, the first winding equivalent circuit includes: the first equivalent resistor is an equivalent resistor of a power supply cable of the motor and a first partial winding of the motor; the second end of the first equivalent inductor is connected with the first end of the first equivalent capacitor and the first end of the second winding equivalent circuit, and the first equivalent inductor is an equivalent inductor of a power supply cable of the motor and a first partial winding of the motor; and the second end of the first equivalent capacitor is connected with the second end of the second winding equivalent circuit and then grounded, and the first equivalent capacitor is the capacitance to ground of the first partial winding of the motor.
In an alternative embodiment, the second winding equivalent circuit includes: the first end of the second equivalent resistor is connected with 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 the second end of the second equivalent resistor is connected with the first end of the second equivalent inductor; the second end of the second equivalent inductor is connected with 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; and the second end of the second equivalent capacitor is connected with the second end of the first equivalent capacitor and then grounded.
In a second aspect, the present invention provides a method for calculating a leakage current parameter of a motor, based on the motor winding equivalent circuit of the first aspect, the method for calculating the leakage current parameter of the motor comprising: obtaining leakage current in a first winding equivalent circuit; calculating the frequency of the leakage current according to the resonance frequency of the leakage current in the first winding equivalent circuit; and calculating the period and the amplitude of the leakage current based on the parameters of the first winding equivalent circuit and the second winding equivalent circuit.
The calculation method of the motor leakage current parameter can accurately analyze and calculate the characteristic parameters such as frequency, amplitude and the like of the leakage current of the aging part, and obtain the variation trend of each characteristic parameter along with the aging degree of the motor, thereby obtaining and predicting the aging degree of the motor.
In an alternative embodiment, the frequency of the leakage current is calculated as:
Wherein f HF is the frequency of the leakage current; l 1 is a first equivalent inductance; c g1 is the first equivalent capacitance.
In an alternative embodiment, the calculation formula of the period of the leakage current is:
Wherein t 0 is the period of the leakage current; l 1 is the first equivalent inductance; c g1 is the first equivalent capacitance; c g2 is a second equivalent capacitance; r p is a third equivalent resistance; the calculation formula of the magnitude of the leakage current is:
Wherein A 0 is the magnitude of the leakage current.
In a third aspect, the present invention provides a method for monitoring insulation aging of a motor, where a power supply end of the motor is connected to an ac side of an inverter, the method comprising: clearing the direct current signal in dead time of the inverter switching the on-off state of the target phase switching tube; after the inverter switches the on-off state of the target phase switching tube, acquiring leakage current of the alternating current side of the inverter; obtaining a frequency, period and amplitude leakage current signal containing leakage current based on the calculation method of the leakage current parameter of the motor in the second aspect; the leakage current signal is attenuated, overturned and integrated to obtain a direct current signal; the insulation aging degree of the motor is evaluated based on the magnitude of the voltage of the direct current signal.
According to the motor insulation aging detection method provided by the invention, the direct current signal is obtained after the attenuation, turnover and integration processing are sequentially carried out on the leakage current signal of the motor, the attenuation speed of the direct current signal is slow, the characteristic information of the leakage current cannot be changed or eliminated in the processing process, the acquisition and the processing are convenient under the condition that the characteristic information of the leakage current is maintained, the detection result is independent of the precision and the current sampling rate of an instrument, and the problem of high current sampling rate required by the traditional monitoring method is solved. And the integrating zero clearing circuit resets and clears the output end of the integrating circuit before the integrating circuit outputs the direct current signal every time, thereby avoiding the influence of the direct current signal when the direct current signal is ensured to be subjected to the last insulation aging detection, and having high signal processing speed and accurate monitoring result. The leakage current signal is processed through the hardware circuit, so that the calculation cost of software is reduced, signal sampling can be directly carried out in the motor controller, and an additional microcontroller is not required to be added. The voltage of leakage current is different due to different insulation aging degrees, and the direct current signal voltage with low attenuation speed is easy to collect and detect, so that the insulation aging degree of the motor can be evaluated rapidly through the direct current signal voltage.
In a fourth aspect, the present invention provides an insulation degradation monitoring circuit for implementing the monitoring method of the third aspect, the circuit comprising: the system comprises a current sensor, a signal attenuation circuit, a multiplier, an integrating circuit, an integrating zero clearing circuit and a controller, wherein the current sensor is connected with a power supply end of a motor in a non-contact mode, and an output end of the current sensor is connected with an input end of the signal attenuation circuit and is used for outputting leakage current signals after collecting common mode current of the motor; the input end of the signal attenuation circuit is connected with the power supply end of the motor, the input end of the signal attenuation circuit receives a leakage current signal of the motor, the output end of the signal attenuation circuit is connected with the input end of the multiplier, and the signal attenuation circuit is used for outputting a first-stage signal after attenuating the leakage current signal to a preset voltage interval; the output end of the multiplier is connected with the input end of the integrating circuit and is used for turning the negative half-period signal of the first-stage signal to the positive half-period and then outputting the second-stage signal; the output end of the integrating circuit is connected with the input end of the controller and is used for integrating the second-stage signal and then outputting a direct current signal; the first output end of the controller is connected with the control end of the inverter, and is used for controlling the on-off state of the switching target phase switching tube of the inverter, outputting a zero clearing signal in the dead time of the on-off state of the switching target phase switching tube of the inverter and evaluating the insulation aging degree of the motor based on the voltage of the direct current signal; and the input end of the integration zero clearing circuit is connected with the second output end of the controller, the input end of the integration zero clearing circuit is connected with a zero clearing signal, and the output end of the integration zero clearing circuit is connected with the output end of the integration circuit and is used for clearing the direct current signal output by the integration circuit based on the zero clearing signal.
The insulation aging detection circuit provided by the invention sequentially carries out attenuation, turnover and integration treatment on the leakage current signal of the equipment to be detected to obtain the direct current signal, the attenuation speed of the direct current signal is slow, the characteristic information of the leakage current can not be changed or eliminated in the treatment process, the acquisition and the treatment are convenient under the condition of keeping the characteristic information of the leakage current, the detection result is independent of the precision and the current sampling rate of an instrument, the problem of high current sampling rate required by the traditional monitoring method is solved, and the aging detection result can be generated only by carrying out attenuation, turnover and integration on the leakage current signal. And the integrating zero clearing circuit resets and clears the output end of the integrating circuit before the integrating circuit outputs the direct current signal every time, thereby avoiding the influence of the direct current signal when the direct current signal is ensured to be subjected to the last insulation aging detection, and having the advantages of high signal processing speed, simple processing process and accurate detection result. The voltage of leakage current is different due to different insulation aging degrees, and the direct current signal voltage with low attenuation speed is easy to collect and detect, so that the insulation aging degree of equipment to be detected can be evaluated rapidly through the direct current signal voltage.
In an alternative embodiment, a signal attenuation circuit includes: the first resistor is connected with the first end of the second resistor and the inverting input end of the first operational amplifier; the second end of the second resistor is connected with the in-phase output end of the first operational amplifier and the input end of the multiplier; the first end of the third resistor is grounded, and the second end of the third resistor is connected with the first end of the fourth resistor and the non-inverting input end of the first operational amplifier; and the second end of the fourth resistor is connected with the inverting output end of the first operational amplifier and the input end of the multiplier.
According to the insulation aging detection circuit provided by the invention, the signal attenuation circuit outputs the attenuated first-stage signal with the amplitude within the preset voltage interval according to the voltage difference value of the two signals at the input end, so that the voltage requirement of the later-stage hardware is met.
In an alternative embodiment, the integrating circuit includes: the first end of the fifth resistor is connected with the output end of the multiplier, and the second end of the fifth resistor is connected with the inverting input end of the second operational amplifier, the first end of the sixth resistor and the first end of the first capacitor; the second end of the sixth resistor is connected with the second end of the first capacitor, the output end of the second operational amplifier and the output end of the integral zero clearing circuit; and the first end of the seventh resistor is grounded, and the second end of the seventh resistor is connected with the non-inverting input end of the second operational amplifier.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a block diagram of one specific circuit of a motor winding equivalent circuit according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method for calculating leakage current parameters of a motor according to an embodiment of the invention;
FIG. 3 is a common mode voltage current plot of a motor according to an embodiment of the invention;
FIG. 4 is an impedance spectrum graph according to an embodiment of the present invention;
FIG. 5 is a flow chart of a motor insulation degradation monitoring method according to an embodiment of the present invention;
fig. 6 is a composition diagram of one specific example of an insulation degradation monitoring circuit according to an embodiment of the present invention;
FIG. 7 is a control timing diagram of an insulation burn-in monitoring circuit according to an embodiment of the invention;
Fig. 8 is a block diagram of one specific circuit of the insulation degradation monitoring circuit according to the embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; the two components can be directly connected or indirectly connected through an intermediate medium, or can be communicated inside the two components, or can be connected wirelessly or in a wired way. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
In addition, the technical features of the different embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The present embodiment provides a motor winding equivalent circuit including: the motor comprises a first winding equivalent circuit 1 and a second winding equivalent circuit 2, wherein the winding component of the motor is divided into two parts, the first part is a first winding connected with a power supply end, and the second part is a residual second winding; the first winding equivalent circuit 1 is connected with a power supply end, the first end is a winding end of the motor, the second end is connected with the first end of the second winding equivalent circuit 2, the third end is connected with the second end of the second winding equivalent circuit 2 and then grounded, and the first winding equivalent circuit 1 is a power supply cable of the motor and an equivalent circuit of the first winding; the second winding equivalent circuit 2 is an equivalent circuit of the second winding.
Specifically, as shown in fig. 1, the first winding equivalent circuit 1 includes: the first equivalent resistor R 9, the first equivalent inductor L 1 and the first equivalent capacitor C g1, wherein the first end of the first equivalent resistor R 9 is a winding end W of the motor, the second end of the first equivalent resistor R 9 is connected with the first end of the first equivalent inductor L 1, and the first equivalent resistor R 9 is an equivalent resistor of a power supply cable of the motor and a first partial winding of the motor; the second end of the first equivalent inductor L 1 is connected with the first end of the first equivalent capacitor C g1 and the first end of the second winding equivalent circuit 2, and the first equivalent inductor L 1 is the equivalent inductor of a power supply cable of the motor and a first partial winding of the motor; and the second end of the first equivalent capacitor C g1 is connected with the second end of the second winding equivalent circuit 2 and then grounded, and the first equivalent capacitor is the capacitance to ground of the first partial winding of the motor.
Specifically, as shown in fig. 1, the second winding equivalent circuit 2 includes: the second equivalent resistor R 10, the second equivalent inductor L 2, the second equivalent capacitor C g2, the third equivalent resistor R p and the third equivalent capacitor C p, wherein the first end of the second equivalent resistor R 10 is connected with the first end of the third equivalent resistor R p, the first end of the third equivalent capacitor C p and the second end of the first equivalent inductor L 1, and the second end of the second equivalent resistor R 10 is connected with the first end of the second equivalent inductor L 2; the second end of the second equivalent inductor L 2 is connected with the second end of the third equivalent resistor R p, the second end of the third equivalent capacitor C p and the first end of the second equivalent capacitor C g2; the second end of the second equivalent capacitor C g2 is connected to the second end of the first equivalent capacitor C g1 and then grounded.
Illustratively, in fig. 1, where W is the motor winding end, G is ground (or the casing), the common mode voltage is generally greatest at the winding end, and the electrical stress is greatest, so the winding end is the location where the insulation degradation to ground is most severe for the entire motor winding. Therefore, the leakage current flowing through the winding wire end is analyzed, the condition of the motor leakage current can be obtained, and the insulation aging degree of the motor is evaluated.
In order to provide theoretical reference for insulation aging detection, the motor winding equivalent circuit provided by the embodiment constructs a motor winding equivalent circuit model, and the parts easy to age are equivalent to a first winding equivalent circuit, so that the follow-up calculation and analysis are convenient.
The present embodiment provides a method for calculating a motor leakage current parameter, which is calculated based on the motor winding equivalent circuit of the above embodiment, as shown in fig. 2, and includes:
step S1: and obtaining leakage current in the first winding equivalent circuit.
For example, referring to fig. 1, since the first equivalent capacitor C g1 represents an equivalent capacitor to ground near the terminal, the parameters of the first equivalent resistor R 9, the first equivalent inductor L 1, and the first equivalent capacitor C g1 are far smaller than the parameters of the second equivalent resistor R 10, the second equivalent inductor L 2, and the second equivalent capacitor C g2, and thus, the high-frequency current generated by the switch at the motor power supply terminal generally flows to ground through the first equivalent capacitor C g1, so it can be considered that the high-frequency leakage current in the first winding equivalent circuit is sensitive to the insulation aging change.
Step S2: and calculating the frequency of the leakage current according to the resonance frequency of the leakage current in the first winding equivalent circuit.
It should be noted that, in fig. 1, in the actual motor, the first equivalent capacitance C g1 in the equivalent model is far smaller than the second equivalent capacitance C g2, the first equivalent inductance L 1 is far smaller than the second equivalent inductance L 2, the first equivalent resistance R 9 is far smaller than the second equivalent resistance R 10, and the influence of the inductance of the resistance in the circuit on the motor impedance is far greater than the resistance under high frequency, and the following all calculation formulas are obtained by combining the actual motor parameters, simplifying and omitting the small magnitude terms in the formulas.
Illustratively, referring to fig. 1, after obtaining the high-frequency leakage current in the first winding equivalent circuit, the frequency f HF of the leakage current is:
Step S3: and calculating the period and the amplitude of the leakage current based on the parameters of the second winding equivalent circuit.
Illustratively, the common mode voltage pattern of the motor is shown in fig. 3, the waveform motor in the box is the common mode voltage pattern before and after the IGBT of either phase is turned on, and 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 plateau form, where τ represents the voltage rise time. U (t) is expressed as follows:
u (t) is transformed by Law to give U(s) as follows:
the high frequency current response I HF(s) can be expressed as follows:
Wherein Z CM(s) is high-frequency impedance, and the calculation formula is as follows:
The waveform of the waveform i HF of the high-frequency current response is:
wherein, each phase parameter p 1～p3 is:
Wherein, parameter a is:
wherein, angular velocity ω is:
The parameters of the equivalent model determine the parameters of the leakage current, such as the leakage current period t 0 and the magnitude a 0, and the relationship between the components in the model are shown below. The decrease of C g1 on insulation aging will lead to the decrease of t 0 and the decrease of A 0, the specific relation is as follows:
Illustratively, parameter extraction of the motor model is performed based on the equivalent circuit shown in fig. 1 and an actual one 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 equivalent circuit impedance spectrum are shown in fig. 4, so that the two have good coincidence, and the equivalent model can better simulate the two common mode resonance point valley values of the actual motor. The two resonance points are designated MFTR and HFTR, respectively, wherein HFTR is the frequency and impedance corresponding to the leakage current generated by the switch.
TABLE 1
| Resistor | Resistance value | Inductance | Inductance value | Capacitance device | Capacitance value |
| R9 | 1(mΩ) | L1 | 1.4(uH) | Cg1 | 1.1(nF) |
| R10 | 10(mΩ) | L2 | 30(uH) | Cg2 | 11.9(nF) |
| Rp | 80(Ω) | Cp | 0.1(nF) |
The calculation method of the motor leakage current parameter can accurately analyze and calculate the characteristic parameters such as frequency, amplitude and the like of the leakage current of the aging part, and obtain the variation trend of each characteristic parameter along with the aging degree of the motor, thereby obtaining and predicting the aging degree of the motor.
The embodiment provides a method for monitoring insulation aging of a motor, as shown in fig. 5, wherein a power supply end of the motor is connected with an ac side of an inverter, and the method comprises the following steps:
step S4: and clearing the direct current signal in dead time for the inverter to switch the on-off state of the target phase switching tube.
Step S5: and after the inverter switches the on-off state of the target phase switching tube, acquiring leakage current of the alternating current side of the inverter.
Step S6: based on the above embodiments and the calculation method of the motor leakage current parameter according to any of the alternative embodiments, the frequency, period and amplitude leakage current signal including the leakage current is obtained.
Step S7: and carrying out attenuation, overturning and integration processing on the leakage current signal to obtain a direct current signal.
Step S8: the insulation aging degree of the motor is evaluated based on the magnitude of the voltage of the direct current signal.
Illustratively, the inverter switches the switching states of the upper and lower tubes of the target phase, thereby switching the power supply state to the motor. Taking the example of the switching off of a lower tube and the switching on of an upper tube of an inverter target phase: the method comprises the steps that leakage current is generated on an alternating current side of an inverter at the moment of upper tube conduction, a direct current signal output by last insulation aging monitoring is cleared when a lower tube of a target phase is turned off, a motor winding equivalent circuit is utilized and a calculation method of leakage current parameters of the motor is combined, after the leakage current signal containing the frequency, period and amplitude of the leakage current is obtained, attenuation, turnover and integration processing are sequentially carried out on the leakage current signal, after an original leakage current waveform is completely attenuated to 0, a direct current signal with a lower attenuation speed is obtained, the direct current signal is sampled, the direct current signal size reflects the aging degree of motor insulation, the direct current signal is sampled for multiple times, an average value is calculated, and the insulation aging degree of the motor is estimated according to the calculated result.
It should be noted that, after sampling, data screening is performed, and the sampling result satisfying the following conditions may be retained as a state evaluation basis:
(1) The inverter target phase switching operation period of the insulation state monitoring has no switching operation of other phases.
(2) The target phase on time is not less than the time for the original leakage current to decay to 0.
(3) The phase current of the target phase at the sampling instant is > 0.
It should be noted that motors include, but are not limited to, single phase motors, open winding motors, and multi-phase motors.
According to the motor insulation aging detection method, the direct current signal is obtained after the attenuation, turnover and integration processing of the leakage current signal of the motor are sequentially carried out, the attenuation speed of the direct current signal is slow, the characteristic information of the leakage current cannot be changed or eliminated in the processing process, the acquisition and the processing are convenient under the condition that the characteristic information of the leakage current is kept, the detection result is independent of the precision of an instrument and the current sampling rate, and the problem of high current sampling rate required by a traditional monitoring method is solved. And the integrating zero clearing circuit resets and clears the output end of the integrating circuit before the integrating circuit outputs the direct current signal every time, thereby avoiding the influence of the direct current signal when the direct current signal is ensured to be subjected to the last insulation aging detection, and having high signal processing speed and accurate monitoring result. The leakage current signal is processed through the hardware circuit, so that the calculation cost of software is reduced, signal sampling can be directly carried out in the motor controller, and an additional microcontroller is not required to be added. The voltage of leakage current is different due to different insulation aging degrees, and the direct current signal voltage with low attenuation speed is easy to collect and detect, so that the insulation aging degree of the motor can be evaluated rapidly through the direct current signal voltage.
The present 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 integrating circuit 33, an integrating clear circuit 34, a controller 35 and a current sensor 36.
As shown in fig. 6, the current sensor 36 is connected to the power supply terminal of the motor in a non-contact manner, and its output terminal is connected to the input terminal of the signal attenuation circuit 31, and is used for collecting the common mode current of the motor and outputting a leakage current signal.
As shown in fig. 6, the output end of the signal attenuation circuit 31 is connected to the input end of the multiplier 32, and is used for attenuating the leakage current signal to a preset voltage range and then outputting a first-stage signal.
As shown in fig. 6, the output of the multiplier 32 is connected to the input of the integrating circuit 33, which is used to invert 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 fig. 6, the output terminal of the integrating circuit 33 is connected to the input terminal of the controller 35, and is configured to integrate the second-stage signal and output the dc signal Uo.
As shown in fig. 6, the first output terminal of the controller 35 is connected to the control terminal of the inverter, and is configured to control the on-off state of the inverter switching target phase switching tube, output a clear signal in the dead time of the on-off state of the inverter switching target phase switching tube, and evaluate the insulation aging degree of the motor based on the voltage of the dc signal Uo.
As shown in fig. 6, the input end of the integration zero clearing circuit 34 is connected to the second output end of the controller 35, the input end thereof receives the zero clearing signal, and the output end thereof is connected to the output end of the integration circuit 33, and is used for clearing the direct current signal output by the integration circuit based on the zero clearing signal.
As an example, referring to fig. 6 and 7, taking the example that the controller 35 controls the lower tube and the upper tube of the inverter target phase to be turned off, the controller 35 sends a clear signal to the integral clear circuit 34 in the dead time when the lower tube is turned off and the upper tube is not turned on, so that the integral clear circuit 34 resets the output voltage of the integral circuit 33 based on the clear signal. The leakage current signal of the motor is a decaying sine signal.
Illustratively, in fig. 6, the power supply cables of the windings of each phase of the motor pass through the current sensor 36, so that the magnetic field of the load current of each phase is cancelled during normal operation, 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.
For example, referring to fig. 6 and fig. 7, when the signal attenuation circuit 31 collects the leakage current signal, the leakage current signal includes characteristic information such as frequency, period, amplitude, etc. of the leakage current, the signal attenuation circuit 31 attenuates the leakage current signal to a preset voltage interval so as to adapt to the voltage requirement of the post-stage circuit, and the damage of the hardware of the post-stage circuit caused by the too high voltage amplitude is avoided. The multiplier 32 inverts the negative half period of the first-stage signal output from the signal attenuating circuit 31 to the positive half period, and outputs a second-stage signal, and the integrating circuit 33 integrates the second-stage signal to change the second-stage signal into a smooth direct-current signal Uo with a slow attenuation speed. The controller 35 evaluates the insulation aging degree of the motor by comparing the output direct current signal Uo with the parameter of the motor when leaving the factory.
Illustratively, in fig. 6, the controller 35 may also perform data transmission with a terminal, such as a computer PC, through which a user may send control instructions to the controller 35 or receive insulation degradation monitoring results of the motor returned by the controller 35.
The insulation aging detection circuit provided by the invention sequentially carries out attenuation, turnover and integration treatment on the leakage current signal of the equipment to be detected to obtain the direct current signal, the attenuation speed of the direct current signal is slow, the characteristic information of the leakage current can not be changed or eliminated in the treatment process, the acquisition and the treatment are convenient under the condition of keeping the characteristic information of the leakage current, the detection result is independent of the precision and the current sampling rate of an instrument, the problem of high current sampling rate required by the traditional monitoring method is solved, and the aging detection result can be generated only by carrying out attenuation, turnover and integration on the leakage current signal. And the integrating zero clearing circuit resets and clears the output end of the integrating circuit before the integrating circuit outputs the direct current signal every time, thereby avoiding the influence of the direct current signal when the direct current signal is ensured to be subjected to the last insulation aging detection, and having the advantages of high signal processing speed, simple processing process and accurate detection result. The voltage of leakage current is different due to different insulation aging degrees, and the direct current signal voltage with low attenuation speed is easy to collect and detect, so that the insulation aging degree of equipment to be detected can be evaluated rapidly through the direct current signal voltage.
In some alternative embodiments, as shown in fig. 8, the signal attenuation circuit 31 includes: the first resistor R 1, the second resistor R 2, the third resistor R 3, the fourth resistor R 4 and the first operational amplifier U 1, wherein the first end of the first resistor R 1 inputs leakage current signals, and the second end of the first resistor R 1 is connected with the first end of the second resistor R 2 and the inverting input end of the first operational amplifier U 1; a second end of the second resistor R 2 is connected to the in-phase output end of the first operational amplifier U 1 and the input end of the multiplier 32; the first end of the third resistor R 3 is grounded, and the second end of the third resistor R 3 is connected with the first end of the fourth resistor R 4 and the non-inverting input end of the first operational amplifier U 1; the second terminal of the fourth resistor R 4 is connected to the inverting output terminal of the first operational amplifier U 1 and the input terminal of the multiplier 32.
As shown in fig. 8, the integrating 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 a first end of the fifth resistor R 5 is connected to the output end of the multiplier 32, and a second end thereof is 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; a second end of the sixth resistor R 6 is connected to the second end of the first capacitor C 1 and the output end of the second operational amplifier U 2; the first end of the seventh resistor R 7 is grounded, and the second end of the seventh resistor R 7 is connected with the non-inverting input end of the second operational amplifier U 2.
Illustratively, in FIG. 8, the integral clearance circuit 34 includes: the inverting input terminal of the third operational amplifier U 3 is connected to the output terminal thereof and the output terminal of the second operational amplifier U 2, the enable terminal thereof receives the clear zero signal, and the non-inverting input terminal thereof is grounded. When the controller 35 sends out a zero clearing signal, the third operational amplifier U 3 outputs a voltage of 0V, so as to zero the dc signal Uo at the output end of the second operational amplifier U 2.
Specifically, in fig. 8, the leakage current signal is a sine wave signal with a relatively fast attenuation 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, and the first operational amplifier U 1 attenuates the signal difference between the non-inverting input terminal and the inverting input terminal and outputs the first-stage signal. The multiplier 32 squares the first-stage signal, and after the first-stage signal is turned over from the negative half period to the positive half period, the integration circuit 33 performs integration processing to output a dc signal Uo having a slow decay rate.
Specifically, in fig. 8, the integrating and zeroing circuit 34 collects a zeroing signal at the same time when each insulation aging detection starts, and when the zeroing signal is high, the third operational amplifier U 3 outputs a voltage of 0V, so as to zero the dc signal Uo at the output end of the second operational amplifier U 2, and clear the result of the last insulation aging detection output.
It should be noted that, referring to fig. 1 and 8, the relationship between the value of the output value U O of the integrating circuit 33 and each parameter of the equivalent circuit in the ideal state is as follows, and the decrease of C g1 during insulation aging will result in the decrease of U O, namely:
For example, when the insulation state of the device to be detected is completely healthy, the voltage of the output signal after the measurement is generally equal to the voltage recorded by the measurement at the time of shipment; as the voltage of the output signal of the device to be tested will gradually decrease, severe degradation of the insulation is identified, or there is a potential risk of failure, when the voltage of the output signal decreases to 70% of the original recorded voltage.
Although embodiments of the present invention have been described in connection with the accompanying drawings, various modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope of the invention as defined by the appended claims.
Claims (10)
1. An electric motor winding equivalent circuit, comprising: a first winding equivalent circuit and a second winding equivalent circuit, wherein,
The winding of the motor is divided into two parts, wherein the first part is a first winding connected with a power supply end, and the second part is a residual second winding;
The first end of the first winding equivalent circuit is connected with the power supply end, the first end of the first winding equivalent circuit is a winding end of the motor, the second end of the first winding equivalent circuit is connected with the first end of the second winding equivalent circuit, the third end of the first winding equivalent circuit is grounded after being connected with the second end of the second winding equivalent circuit, and the first winding equivalent circuit is an equivalent circuit of a power supply cable of the motor and the first winding;
The second winding equivalent circuit is an equivalent circuit of the second winding.
2. The electric machine winding equivalent circuit of claim 1, wherein the first winding equivalent circuit comprises: a first equivalent resistance, a first equivalent inductance and a first equivalent capacitance, wherein,
The first end of the first equivalent resistor is a winding end of the motor, the second end of the first equivalent resistor is connected with the first end of the first equivalent inductor, and the first equivalent resistor is an equivalent resistor of a power supply cable of the motor and a first partial winding of the motor;
the second end of the first equivalent inductor is connected with 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 inductor of a power supply cable of the motor and a first partial winding of the motor;
And the second end of the first equivalent capacitor is connected with the second end of the second winding equivalent circuit and then grounded, and the first equivalent capacitor is the capacitance to ground of the first partial winding of the motor.
3. The electric motor winding equivalent circuit of claim 2, wherein the second winding equivalent circuit comprises: a second equivalent resistance, a second equivalent inductance, a second equivalent capacitance, a third equivalent resistance and a third equivalent capacitance, wherein,
The first end of the second equivalent resistor is connected with 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 the second end of the second equivalent resistor is connected with the first end of the second equivalent inductor;
The second end of the second equivalent inductor is connected with 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;
and the second end of the second equivalent capacitor is connected with 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 the following steps:
obtaining leakage current in a first winding equivalent circuit;
calculating the frequency of the leakage current according to the resonance frequency of the leakage current in the first winding equivalent circuit;
and calculating the period and the amplitude of the leakage current based on the parameters of the first winding equivalent circuit and the second winding equivalent circuit.
5. The method for calculating leakage current parameters of a motor according to claim 4, wherein,
The calculation formula of the frequency of the leakage current is as follows:
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 leakage current parameters of a motor according to claim 5, wherein,
The calculation formula of the period of the leakage current is as follows:
Wherein t 0 is the period of the leakage current; l 1 is the first equivalent inductance; c g1 is the first equivalent capacitance; c g2 is the second equivalent capacitance; r p is the third equivalent resistance;
The calculation formula of the amplitude of the leakage current is as follows:
Wherein A 0 is the magnitude of the leakage current.
7. A method for monitoring insulation degradation of a motor, wherein a power supply terminal of the motor is connected to an ac side of an inverter, the method comprising:
clearing the direct current signal in dead time of the inverter switching the on-off state of the target phase switching tube;
After the inverter switches the on-off state of the target phase switching tube, acquiring leakage current of the alternating current side of the inverter;
Obtaining a frequency, period and amplitude leakage current signal containing leakage current based on the calculation method of the leakage current parameter of the motor according to any one of claims 4 to 6;
The leakage current signal is attenuated, overturned and integrated to obtain a direct current signal;
and evaluating the insulation aging degree of the motor based on the voltage of the direct current signal.
8. An insulation degradation monitoring circuit for implementing the monitoring method of claim 7, the circuit comprising: a current sensor, a signal attenuation circuit, a multiplier, an integration circuit, an integration zero clearing circuit and a controller, wherein,
The current sensor is connected with the power supply end of the motor in a non-contact mode, the output end of the current sensor is connected with the input end of the signal attenuation circuit, and the current sensor is used for collecting common mode current of the motor and then outputting leakage current signals;
the output end of the signal attenuation circuit is connected with the input end of the multiplier and is used for outputting a first-stage signal after attenuating the leakage current signal to a preset voltage interval;
The output end of the multiplier is connected with the input end of the integrating circuit and is used for outputting a second-stage signal after the negative half-period signal of the first-stage signal is overturned to the positive half-period;
the output end of the integrating circuit is connected with the input end of the controller and is used for integrating the second-stage signal and then outputting a direct current signal;
The first output end of the controller is connected with the control end of the inverter, and is used for controlling the on-off state of the switching target phase switching tube of the inverter, outputting a zero clearing signal in the dead time of the on-off state of the switching target phase switching tube of the inverter, and evaluating the insulation aging degree of the motor based on the voltage of the direct current signal;
And the input end of the integral zero clearing circuit is connected with the second output end of the controller, the input end of the integral zero clearing circuit is used for receiving a zero clearing signal, the output end of the integral zero clearing circuit is connected with the output end of the integral circuit, and the integral zero clearing circuit is used for clearing the direct current signal output by the integral circuit based on the zero clearing signal.
9. The insulation degradation monitoring circuit of claim 8, wherein the signal attenuation circuit comprises: a first resistor, a second resistor, a third resistor, a fourth resistor and a first operational amplifier,
The first end of the first resistor is input with the leakage current signal, and the second end of the first resistor is connected with the first end of the second resistor and the inverting input end of the first operational amplifier;
the second end of the second resistor is connected with the in-phase output end of the first operational amplifier and the input end of the multiplier;
The first end of the third resistor is grounded, and the second end of the third resistor is connected with the first end of the fourth resistor and the non-inverting input end of the first operational amplifier;
And the second end of the fourth resistor is connected with the inverting output end of the first operational amplifier and the input end of the multiplier.
10. The insulation degradation monitoring circuit of claim 8, wherein the integrating circuit comprises: a fifth resistor, a sixth resistor, a seventh resistor, a first capacitor and a second operational amplifier,
A fifth resistor, a first end of which is connected with the output end of the multiplier, and a second end of which is connected with 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, the second end of which is connected with the second end of the first capacitor, the output end of the second operational amplifier and the output end of the integral zero clearing circuit;
and the first end of the seventh resistor is grounded, and the second end of the seventh resistor is connected with the non-inverting input end of the second operational amplifier.
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