CN109613365B - A method and system for on-line evaluation of the state of electrolytic capacitors - Google Patents
A method and system for on-line evaluation of the state of electrolytic capacitors Download PDFInfo
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Abstract
The invention discloses an electrolytic capacitor state online evaluation method and system, which achieve the purpose of evaluating the health state of an electrolytic capacitor online without depending on a system structure. The method comprises the following steps: acquiring temperature characteristics of Equivalent Series Resistance (ESR) of a plurality of target electrolytic capacitors along with temperature change and frequency characteristics of the ESR and impedance along with operating frequency change, and determining a fitting model of the ESR of the target electrolytic capacitors along with the temperature change in a specific operating frequency range according to the temperature characteristics and the frequency characteristics; determining the initial ESR of the electrolytic capacitor to be tested according to the online running temperature of the electrolytic capacitor to be tested and the fitting model; obtaining a voltage ripple and a current ripple of the electrolytic capacitor to be detected on line, and determining real-time ESR of the electrolytic capacitor to be detected according to the voltage ripple and the current ripple; and evaluating the state of the electrolytic capacitor to be tested according to the initial ESR and the real-time ESR.
Description
Technical Field
The invention belongs to the technical field of electronic component testing, and particularly relates to an electrolytic capacitor state online evaluation method and system.
Background
The electrolytic capacitor is widely applied to systems such as a power converter, a switching power supply, a frequency converter and the like by virtue of the characteristics of large energy density, high capacity and low price, meanwhile, the electrolytic capacitor also becomes one of the weakest parts of the system by virtue of an electrochemical working principle, and the whole system is possibly broken down due to unpredictable faults. Fig. 1 shows a percentage failure rate distribution of components in a switching power supply system. Therefore, it is necessary to research the loss mechanism of the electrolytic capacitor, evaluate the health status of the electrolytic capacitor, accurately predict the fault in time and perform preventive maintenance so as to reduce the system shutdown and maintenance cost.
The deterioration of the electrolytic capacitor is mainly manifested by the volatilization of the electrolyte, which also results in an increase in the Series Equivalent Resistance (ESR) and a decrease in the capacitance of the electrolytic capacitor. The state of health of the electrolytic capacitor can be evaluated by the ESR of the electrolytic capacitor.
The ESR-based state evaluation method of the electrolytic capacitor may be classified into an off-line method and an on-line method. The off-line mode depends on the precision of the measuring component, and the capacitor can be taken down to complete the measurement only when the system where the electrolytic capacitor is located is in an off-line state, so that the measurement is inconvenient. The online mode in the prior art generally depends on a system structure, and has a small application range and complex implementation.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an electrolytic capacitor state online evaluation method and system, which achieve the purpose of evaluating the health state of an electrolytic capacitor online without depending on the system structure.
The embodiment of the invention provides an electrolytic capacitor state online evaluation method, which comprises the following steps:
acquiring temperature characteristics of Equivalent Series Resistance (ESR) of a plurality of target electrolytic capacitors along with temperature change and frequency characteristics of the ESR and impedance along with operating frequency change, and determining a fitting model of the ESR of the target electrolytic capacitors along with the temperature change in a specific operating frequency range according to the temperature characteristics and the frequency characteristics; wherein, in the specific operating frequency range, the impedance of the target electrolytic capacitor in the frequency characteristic is mainly expressed as ESR;
determining the initial ESR of the electrolytic capacitor to be tested according to the online running temperature of the electrolytic capacitor to be tested and the fitting model; wherein the electrolytic capacitor to be tested has the same specification as the target electrolytic capacitor;
obtaining a voltage ripple and a current ripple of the electrolytic capacitor to be detected on line, and determining real-time ESR of the electrolytic capacitor to be detected according to the voltage ripple and the current ripple;
and evaluating the state of the electrolytic capacitor to be tested according to the initial ESR and the real-time ESR.
In one possible embodiment, the acquiring the temperature characteristics of ESR versus temperature and the frequency characteristics of ESR and impedance versus operating frequency of a plurality of target electrolytic capacitors includes:
under the same operating frequency, obtaining ESR of the target electrolytic capacitor at different temperatures, and obtaining the temperature characteristic of the ESR of the target electrolytic capacitor along with temperature change;
and acquiring ESR and Z of the target electrolytic capacitor at different operating frequencies at a set temperature to obtain the frequency characteristics of the ESR and the impedance of the target electrolytic capacitor along with the variation of the operating frequencies.
In one possible embodiment, the determining the fitted model of the ESR of the target electrolytic capacitor as a function of temperature in the specific operating frequency range based on the temperature characteristic and the frequency characteristic includes:
determining the specific operating frequency range at which the impedance of the target electrolytic capacitor exhibits ESR, from the temperature characteristic and the frequency characteristic;
determining the fitted model from the particular operating frequency range, the temperature characteristic, and the frequency characteristic.
In one possible embodiment, the determining the initial ESR of the electrolytic capacitor under test according to the on-line operating temperature of the electrolytic capacitor under test and the fitted model includes:
determining constant parameters of a fitting model formula of the initial ESR of the electrolytic capacitor to be tested based on the fitting model;
and determining the initial ESR of the electrolytic capacitor to be measured according to the operating temperature and the fitting model formula after the constant parameters are initialized.
In one possible embodiment, the fitted model formula of the initial ESR of the electrolytic capacitor under test is as follows:
ESRS＝A+Be-T/C； (1)
wherein ESRSIs the initial ESR; A. b and C are the constant parameters; t is the operating temperature; e is a natural index.
In one possible embodiment, the determining the real-time ESR of the electrolytic capacitor under test according to the voltage ripple and the current ripple includes:
and extracting a voltage harmonic component and a current harmonic component in the voltage ripple and the current ripple within the specific operating frequency range by using a high-pass filter, and determining the real-time ESR of the electrolytic capacitor to be tested according to the extracted voltage harmonic component and the extracted current harmonic component.
In one possible embodiment, the determining the real-time ESR of the electrolytic capacitor under test from the extracted voltage harmonic component and the extracted current harmonic component includes:
and determining a voltage harmonic component effective value according to the voltage harmonic component, determining a current harmonic component effective value according to the current harmonic component, and determining the real-time ESR according to the ratio of the voltage harmonic component effective value to the current harmonic component effective value.
In a possible embodiment, said real-time ESR is determined according to a ratio of said voltage harmonic component effective value to said current harmonic component effective value, using the following formula:
ESRa＝vcf-rms/icf-rms； (4)
wherein v iscfIs the voltage ripple; v. ofcf-rmsIs the effective value of the voltage harmonic component; i.e. icfIs the current ripple component; i.e. icf-rmsIs the effective value of the current harmonic component; the ESRaIs the real-time ESR.
In one possible embodiment, said evaluating the state of said electrolytic capacitor under test as a function of said initial ESR and said real-time ESR comprises:
evaluating the state of the electrolytic capacitor to be tested according to the ratio alpha of the real-time ESR to the initial ESR, and if alpha is more than or equal to 1 and less than 2, determining that the electrolytic capacitor to be tested is in a good health state; if alpha is more than or equal to 2 and less than 3, determining that the electrolytic capacitor to be tested is in a normal state; and if the alpha is more than or equal to 3, determining that the electrolytic capacitor to be tested is poor in health state.
The embodiment of the invention also provides an electrolytic capacitor state online evaluation system, which comprises:
the characteristic detection module is used for acquiring the temperature characteristic of Equivalent Series Resistance (ESR) of the target electrolytic capacitors along with the temperature change and the frequency characteristic of the ESR and the impedance along with the operation frequency change;
a fitting model module for determining a fitting model of the ESR of the target electrolytic capacitor as a function of temperature within a specific operating frequency range, based on the temperature characteristic and the frequency characteristic; wherein, in the specific operating frequency range, the impedance of the target electrolytic capacitor in the frequency characteristic is mainly expressed as ESR;
the initial ESR determining module is used for determining the initial equivalent series resistance of the electrolytic capacitor to be tested according to the online running temperature of the electrolytic capacitor to be tested and the fitting model; wherein the electrolytic capacitor to be tested has the same specification as the target electrolytic capacitor;
the online detection module is used for acquiring the voltage ripple and the current ripple of the electrolytic capacitor to be detected online;
the real-time ESR determining module is used for determining real-time ESR of the electrolytic capacitor to be tested according to the voltage ripple and the current ripple;
and the evaluation module is used for evaluating the state of the electrolytic capacitor to be tested according to the initial ESR and the real-time ESR.
The invention has the beneficial effects that: according to the temperature characteristic and the frequency characteristic of Equivalent Series Resistance (ESR) of a plurality of target electrolytic capacitors with the same specification as the electrolytic capacitor to be tested along with the change of temperature and operating frequency respectively and the frequency characteristic of Z along with the change of frequency, obtaining a specific frequency range of the electrolytic capacitor with the specification, wherein Z mainly represents ESR, and the fitting model of the ESR along with the change of temperature in the specific operating frequency range, so that the initial ESR of the electrolytic capacitor to be tested can be determined according to the online operating temperature of the electrolytic capacitor to be tested and the fitting model; and then according to the online voltage ripple and the current ripple of obtaining the electrolytic capacitor that awaits measuring confirm the real-time ESR of the electrolytic capacitor that awaits measuring, according to initial ESR with real-time ESR can real-time aassessment the health status of electrolytic capacitor that awaits measuring realizes not relying on system architecture and on-line aassessment the purpose of the health status of electrolytic capacitor.
Drawings
FIG. 1 is a schematic diagram of the percentage distribution of failure rates of components in a prior art switching power supply system;
FIG. 2 is a flow chart of an online evaluation method for the state of an electrolytic capacitor according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram of an equivalent circuit of an electrolytic capacitor provided in an embodiment of the present application;
FIG. 4 is a simplified equivalent circuit schematic diagram of an electrolytic capacitor provided in an embodiment of the present application;
fig. 5 is a schematic diagram of the ESR temperature characteristic of the present application according to the temperature variation;
fig. 6 is a schematic diagram of frequency characteristics of ESR as a function of operating frequency according to an embodiment of the present application;
fig. 7 is a schematic diagram of a fitting model obtained according to temperature characteristics and frequency characteristics provided in an embodiment of the present application;
FIG. 8 is a schematic diagram of an online evaluation system for the state of an electrolytic capacitor according to an embodiment of the present disclosure;
fig. 9 is a schematic diagram of a real-time monitoring system provided in an embodiment of the present application;
FIG. 10 is a schematic circuit diagram of voltage sampling according to an embodiment of the present disclosure;
FIG. 11 is a schematic diagram of electrical temperature acquisition provided by an embodiment of the present application;
fig. 12 is a schematic circuit diagram of a Boost circuit according to an embodiment of the present disclosure;
fig. 13 is a schematic structural diagram of a real-time monitoring system using a Boost circuit according to an embodiment of the present disclosure;
fig. 14 is a schematic diagram of voltage ripples at two ends of the electrolytic capacitor 1 provided in the embodiment of the present application;
fig. 15 is a schematic diagram of a current ripple flowing through the electrolytic capacitor 1 according to an embodiment of the present application;
fig. 16 is a schematic diagram showing an ESR of an electrolytic capacitor 1 provided in an example of the present application;
fig. 17 is a schematic view of the health state of the electrolytic capacitor 1 provided in the embodiment of the present application.
Detailed Description
The above description is only for the purpose of illustrating the present invention and is not intended to limit the scope of the present invention. All equivalent changes and modifications made according to the spirit of the main technical scheme of the invention are to be covered within the scope of the invention.
Referring to fig. 2, an embodiment of the present invention provides an online electrolytic capacitor state evaluation method, including:
acquiring temperature characteristics of ESR of a plurality of target electrolytic capacitors changing along with temperature and frequency characteristics of ESR and impedance changing along with operating frequency, and determining a fitting model of the ESR of the target electrolytic capacitors changing along with temperature in a specific operating frequency range according to the temperature characteristics and the frequency characteristics; among them, in a specific operating frequency range, the impedance of the target electrolytic capacitor in the frequency characteristic is mainly expressed as ESR.
202, determining the initial ESR of the electrolytic capacitor to be tested according to the online running temperature of the electrolytic capacitor to be tested and the fitting model; wherein the electrolytic capacitor to be measured has the same specification as the target electrolytic capacitor.
And 203, acquiring the voltage ripple and the current ripple of the electrolytic capacitor to be measured on line, and determining the real-time ESR of the electrolytic capacitor to be measured according to the voltage ripple and the current ripple.
And 204, evaluating the state of the electrolytic capacitor to be tested according to the initial ESR and the real-time ESR.
The plurality of target electrolytic capacitors may be understood as target electrolytic capacitors of the same brand, the same specification and in a brand new state, and the electrolytic capacitor to be measured and the target electrolytic capacitors should be of the same brand and the same specification.
In this embodiment, a fitting model of the ESR of the electrolytic capacitor of the brand specification varying with the temperature in the specific operating frequency range is obtained according to the temperature characteristics of the ESR of a plurality of brand-new target electrolytic capacitors of the same brand as the electrolytic capacitor to be measured and the frequency characteristics of the ESR and impedance of the target electrolytic capacitors varying with the operating frequency, so that the initial ESR of the electrolytic capacitor to be measured can be determined according to the operating temperature of the electrolytic capacitor to be measured and the fitting model on line; and then the real-time ESR of the electrolytic capacitor to be detected is determined according to the voltage ripple and the current ripple of the electrolytic capacitor to be detected, the health state of the electrolytic capacitor to be detected can be estimated in real time according to the initial ESR and the real-time ESR, and the purpose of estimating the health state of the electrolytic capacitor on line independent of a system structure is achieved.
In one possible embodiment, the step 201 of obtaining the ESR versus temperature characteristics and the frequency characteristics of the ESR and impedance versus operating frequency of the plurality of target electrolytic capacitors includes:
under the same operating frequency, obtaining ESR of the target electrolytic capacitor at different temperatures, and obtaining the temperature characteristic of the ESR of the target electrolytic capacitor along with the temperature change;
and acquiring the ESR and the impedance Z of the target electrolytic capacitor at different operating frequencies at the set temperature to obtain the frequency characteristics of the ESR and the impedance of the target electrolytic capacitor along with the variation of the operating frequencies.
Therefore, in step 201, different temperatures may be provided by the oven, and ESR of the target electrolytic capacitor at different temperatures may be measured by the measuring instrument, thereby obtaining temperature characteristics. Similarly, a constant temperature may be supplied from an oven to measure the ESR and the frequency characteristics of the impedance of the target electrolytic capacitor at different operating frequencies as a function of the operating frequency.
While the ESR decreases with increasing operating frequency due to energy loss from dipole alignment of the target electrolytic capacitor, the ESR changes little with increasing frequency for electrolytic capacitors in general, and for aluminum electrolytic capacitors in particular. On the other hand, the effective capacitance of the electrolytic capacitor is reduced within the allowable tolerance range due to the reduced permittivity of the electrolytic capacitor. There is thus a frequency point at which the impedance of the electrolytic capacitor behaves predominantly as that of an ideal capacitor and decreases with increasing operating frequency, whereas when the operating frequency is greater than this frequency point, the impedance of the capacitor behaves predominantly as ESR and remains substantially constant. Therefore, fitting of the temperature characteristic and the frequency characteristic can be performed according to the above-described characteristics, and can be expressed by:
ESRS＝A+Be-T/C； (1)
wherein ESRSIs the initial ESR; A. b and C are constant parameters; t is the operating temperature; e is a natural index.
In one possible embodiment, the step 201 of determining a fitting model of ESR of the target electrolytic capacitor varying with temperature in a specific operating frequency range according to the temperature characteristic and the frequency characteristic includes:
determining a specific operating frequency range in which the impedance of the target electrolytic capacitor exhibits ESR, from the frequency characteristics;
a fitting model is determined based on the particular operating frequency range, the temperature characteristic, and the frequency characteristic.
Obviously, the specific operating frequency range is understood herein as a frequency range in which the operating frequency is greater than the frequency point, that is, the impedance is mainly represented as ESR when the operating frequency is greater than the frequency point, and the impedance can be regarded as ESR for easy understanding and analysis.
In one possible embodiment, the step 202 of determining the initial ESR of the electrolytic capacitor under test according to the on-line operating temperature of the electrolytic capacitor under test and the fitted model includes:
determining constant parameters of a fitting model formula of the initial ESR of the electrolytic capacitor to be tested based on the fitting model;
and determining the initial ESR of the electrolytic capacitor to be measured according to the fitting model formula after the operation temperature and the initialization constant parameters.
Namely, the initial ESR of the electrolytic capacitor to be measured is calculated based on the formula (1) and the operating temperature of the electrolytic capacitor to be measured.
It should be noted that the constant parameters A, B and C are obtained from experimental numbers, and are not described in detail herein.
After obtaining the initial ESR of the electrolytic capacitor to be tested according to the electrolytic capacitor with the same specification, a real-time ESR to be compared with the initial ESR is also required, and the real-time ESR in step 203 can be obtained by the following method: and extracting a voltage harmonic component and a current harmonic component in a specific operating frequency range from the voltage ripple and the current ripple by using a high-pass filter, and determining the real-time ESR of the electrolytic capacitor to be detected according to the extracted voltage harmonic component and current harmonic component.
In one possible embodiment, determining the real-time ESR of the electrolytic capacitor under test from the extracted voltage harmonic component and current harmonic component comprises:
and determining a voltage harmonic component effective value according to the voltage harmonic component, determining a current harmonic component effective value according to the current harmonic component, and determining real-time ESR according to the ratio of the voltage harmonic component effective value to the current harmonic component effective value.
In one possible embodiment, the real-time ESR is determined from the ratio of the effective value of the voltage harmonic component to the effective value of the current harmonic component, using the following equation:
ESRa＝vcf-rms/icf-rms； (4)
wherein v iscfIs a voltage ripple; v. ofcf-rmsThe voltage harmonic component effective value; i.e. icfIs the current ripple component; i.e. icf-rmsIs the effective value of the current harmonic component; ESR (equivalent series resistance)aIs real-time ESR.
After determining the initial ESR and the real-time ESR of the electrolytic capacitor under test, different ways may be used for the comparison, and in one possible embodiment, the evaluation of the state of the electrolytic capacitor under test in step 204 based on the initial ESR and the real-time ESR includes:
evaluating the state of the electrolytic capacitor to be tested according to the ratio alpha of the real-time ESR to the initial ESR, and if alpha is more than or equal to 1 and less than 2, determining that the electrolytic capacitor to be tested is in a good health state; if alpha is more than or equal to 2 and less than 3, determining that the electrolytic capacitor to be tested is in a normal state; and if the alpha is more than or equal to 3, determining that the electrolytic capacitor to be tested is poor in health state.
For a clearer understanding of the present invention, the principles involved in the present invention are described in detail as follows:
the electrolytic capacitor includes an electrolytic solution, a metal oxide film, and electrodes (e.g., an anode and a cathode). Generally, the electrolytic capacitor can be represented by different equivalent models under the condition of no working condition, and is relatively comprehensive and reverseAn equivalent circuit mapping the characteristics of the electrolytic capacitor is shown in FIG. 3, wherein R1Is the resistance of the electrode and its lead-out terminal, R2Is the resistance of the electrolyte, R3A resistor and a capacitor C of a metal oxide film1And C2Respectively showing the capacitance of the anode foil and the cathode foil, the diode D is the one-way conductivity of the anode metal gasification film, and the diode L is the equivalent inductance caused by the electrode and the leading terminal thereof. R with very small value can be ignored in practical application3And L, thereby combining R1And R2And C1And C2Thus, a simplified equivalent model is obtained as shown in FIG. 4, where R isESRIs a series equivalent resistance, C0Is an equivalent capacitance.
During the operation of the electrolytic capacitor, the action of the electrolyte directly influences the change of the dielectric property of the metal oxide film, and the internal chemical reaction and electrochemical reaction can repair the metal oxide film, but also influence the quality of the metal oxide film, so that the voltage resistance and the leakage conductivity of the electrolytic capacitor are reduced. Based on the prior art, the electrolytic capacitor is difficult to achieve complete tightness, so that the electrolyte can volatilize, and the volatilization process of the electrolyte can be accelerated by gas generated by internal reaction and temperature rise caused by ripple current. As the electrolyte evaporates, the ESR of the electrolytic capacitor gradually increases, and the relationship is as follows:
wherein, VSDenotes the initial electrolyte volume, VaThe representation shows the electrolyte volume.
When the electrolyte is volatilized from 30 to 40% of its original value, the ESR of the electrolytic capacitor is also increased 2 to 3 times as much as the original value, and the health state of the electrolytic capacitor is treated as a bad state or damaged.
Based on the theory and the idea of the present invention, the ESR is first determined according to the formula (1)S. Since the electrolytic capacitor can be regarded as an ideal capacitance according to the equivalent circuit model of the electrolytic capacitor as shown in FIG. 4And a pure resistor connected in series, the absolute value of the impedance of which is actually the sum of the capacitive reactance and the ESR, and the formula is as follows:
wherein Z is impedance, C0F is the operating frequency, and f is the capacitance of the electrolytic capacitor during operation.
The analysis was as follows: as the operating frequency increases, the ESR decreases due to the energy loss from the dipole alignment, but generally for aluminum electrolytic capacitors, the ESR changes almost little with increasing frequency. It is to be understood that there is a frequency point f0When operating at frequency f<f0When the temperature of the water is higher than the set temperature,
then
That is, the impedance of the electrolytic capacitor is mainly expressed as the impedance of an ideal capacitor, and the impedance Z decreases with increasing frequency; when the operating frequency f is more than or equal to f0When the temperature of the water is higher than the set temperature,
then
That is, the impedance of the electrolytic capacitor is mainly expressed as ESRsAnd remains substantially constant. The initial ESR of the electrolytic capacitor under test can therefore be determined according to this principle.
To verify the above, the aluminum electrolytic capacitor of the same brand, the same specification and brand new type with the parameter of 4500V/2200 μ F and the operating temperature range of-40 ℃ to 85 ℃ is selected in this embodiment, the impedance Z, the ESR value and the capacitance C of the target electrolytic capacitor at different temperatures and different frequencies are measured by the LCR measuring apparatus at the specific temperature provided by the constant temperature box, and the average value of each parameter is taken as the test result. The temperature characteristic shown in fig. 5 and the frequency characteristic shown in fig. 6 were obtained.
Fig. 5 shows the ESR value as a function of temperature at a frequency f of 1000Hz, and fig. 6 shows the impedance Z and ESR values as a function of frequency at a temperature T of 20 ℃. Fig. 5 shows that the ESR of the electrolytic capacitor decreases exponentially with an increase in temperature, and gradually stabilizes. As can be seen from fig. 6, at frequencies less than about 7kHZ, the impedance of the capacitor behaves primarily as the impedance of an ideal capacitor, whereas at frequencies greater than 7kHZ, the impedance of the capacitor behaves primarily as ESR, essentially consistent with theoretical analysis. In addition, since the change of the ESR of the electrolytic capacitor with temperature can be expressed by the formula (1), the experimental data of the ESR of the electrolytic capacitor in the examples was fitted by MATLAB simulation software to obtain a fitting model shown in fig. 7. The constant parameters in equation (1) can be determined from the fitting model shown in fig. 7 as a-8.69, B-43.54, and C-12.30. According to the determined constant parameter, the relative ESR of the temperature point can be calculated as the initial ESR of the electrolytic capacitor to be measured when the operating temperature of the electrolytic capacitor to be measured is obtained.
When the electrolytic capacitor to be tested normally works in the system, the voltage ripple and the current ripple of the electrolytic capacitor to be tested can be extracted on line, and the method is still described by taking the capacitor with the predetermined brand and specification as an example: the switching frequency of a medium-large transmission system is commonly 1-5 kHz, when the voltage ripple frequency of a capacitor is more than 7kHz, the impedance of the capacitor is mainly expressed as ESR, so harmonic components more than 7kHz in voltage ripples and current ripples, such as voltage harmonic component vcf and current harmonic component icf, can be extracted by a high-pass filter, and the effective value v of the voltage harmonic component is calculated according to the formula (2) and the formula (3)cf-rmsAnd the effective value i of the current harmonic componentcf-rmsThus, for an on-line electrolytic capacitor, the real-time ESR can be obtained on-line according to equation (4) based on the above measurements.
Based on the consideration of online real-time evaluation of the state of health of the electrolytic capacitor, corresponding parameters can be set to be associated with the state of health so as to better reflect the evaluation result, for example, the state of the electrolytic capacitor under test is evaluated according to the ratio alpha of the real-time ESR to the initial ESR, and a health parameter H is set. Wherein α is calculated as in equation (7):
α＝ESRa/ESRS； (7)
when alpha is more than or equal to 1 and less than 2, H is 1, the health state of the electrolytic capacitor to be tested is good;
when alpha is more than or equal to 2 and less than 3, H is 2, the health state of the electrolytic capacitor to be tested is general;
and when the alpha is not less than 3 and the H is not more than 3, the health state of the electrolytic capacitor to be tested is poor.
As shown in fig. 8, an embodiment of the present invention further provides an electrolytic capacitor state online evaluation system, including:
a characteristic detection module 801 for acquiring temperature characteristics of ESR with temperature and frequency characteristics of ESR and impedance with operating frequency changes of a plurality of target electrolytic capacitors;
a fitting model module 802 for determining a fitting model of ESR of the target electrolytic capacitor varying with temperature within a specific operating frequency range, based on the temperature characteristic and the frequency characteristic; wherein, in a specific operating frequency range, the impedance of the target electrolytic capacitor in the frequency characteristic is mainly expressed as ESR;
an initial ESR determination module 803, which determines the initial equivalent series resistance of the electrolytic capacitor to be measured according to the online operating temperature of the electrolytic capacitor to be measured and the fitting model; wherein the electrolytic capacitor to be tested has the same specification as the target electrolytic capacitor;
the online detection module 804 is used for online obtaining the voltage ripple and the current ripple of the electrolytic capacitor to be detected;
a real-time ESR determination module 805, configured to determine a real-time ESR of the electrolytic capacitor to be measured according to the voltage ripple and the current ripple;
an evaluation module 806 for evaluating the state of the electrolytic capacitor under test based on the initial ESR and the real-time ESR.
For a better understanding of the present invention, a more specific real-time monitoring system is provided in conjunction with an electrolytic capacitor state online evaluation system, corresponding to the online detection module 804, the real-time ESR determination module 805, and the evaluation module 806. The schematic diagram of the real-time monitoring system is shown in fig. 9, and is explained as follows:
the method mainly comprises the following parts, namely voltage sampling, current sampling, temperature sampling and logic operation. Wherein the voltage sampling can be performed according to the schematic diagram shown in fig. 10, R in fig. 1011And R12Is a voltage-dividing resistor, a capacitor C11Is a voltage transformer T with an isolation capacitor for isolating the DC component in v1 and a transformation ratio of 111The purposes of collecting alternating voltage signals and electrically isolating are achieved; the current sampling can adopt a Rogowski coil to collect current ripples ic of an electrolytic capacitor so as to realize non-invasive sampling; the temperature acquisition can be carried out by acquiring the operating temperature of the electrolytic capacitor through a temperature sensor, as shown in fig. 11; the logic operation can be realized by a dSPACE semi-physical simulation platform, the calculation of the real-time ESR of the electrolytic capacitor is completed, and the output of the health state can be realized. The implementation manner adopted in the embodiment is only for explaining the invention, and the invention is not limited thereto.
In this embodiment, a corresponding test is also performed according to the system shown in fig. 9, where a main circuit is shown in fig. 12, and a system structure using the main circuit of fig. 12 is shown in fig. 13. The main circuit shown in fig. 12 is a Boost (Boost chopper) circuit under an ideal capacitor, and the Boost circuit is widely applied in the field of direct current conversion, such as a photovoltaic system and a power compensation system. In the invention, the parameters of the main components of the Boost circuit are set as follows: the input voltage is 50V, the switching frequency of the mos tube is 5kHz, the duty ratio is 0.75, the load resistance is 100 omega, the electrolytic capacitor adopts the electrolytic capacitor with the same brand and specification, and the working temperature of the electrolytic capacitor is measured by a temperature sensor.
The system test results are as follows:
according to the formulas (2) to (4), the ESR can be calculated using ripple information of the electrolytic capacitor voltage ripple and the current ripple. To complete the completeness of the experiment, two electrolytic capacitors of the same brand were tested in this experiment, wherein the electrolytic capacitor 1 was in a completely new state and the electrolytic capacitor 2 had been subjected to a corresponding aging treatment as a control. Fig. 14 to 17 show experimental test results of the electrolytic capacitor 1, in which the capacitor temperature T is 20 ℃, and the same experimental data for obtaining the electrolytic capacitor 2 are used, and the two electrolytic capacitor data are as follows:
the electrolytic capacitor 1 had an initial ESR of 17.3 m.OMEGA.and a real-time ESR of 19.0 m.OMEGA.
The electrolytic capacitor 2 had an initial ESR of 17.3 m.OMEGA.and a real-time ESR of 55.5 m.OMEGA..
Therefore, the health of the electrolytic capacitor 1 can be judged to be good and the health of the electrolytic capacitor 2 can be judged to be normal according to the formula (7).
In the embodiment of the application, a fitting model of the ESR of the electrolytic capacitor with the brand specification changing with the temperature in the specific operating frequency range is obtained according to the temperature characteristics of the ESR of a plurality of brand-new target electrolytic capacitors with the same brand and the same specification as the electrolytic capacitor to be tested and the frequency characteristics of the ESR and the impedance of the target electrolytic capacitors changing with the operating frequency, so that the initial ESR of the electrolytic capacitor to be tested can be determined according to the online operating temperature of the electrolytic capacitor to be tested and the fitting model; and then the real-time ESR of the electrolytic capacitor to be detected is determined according to the voltage ripple and the current ripple of the electrolytic capacitor to be detected, the health state of the electrolytic capacitor to be detected can be estimated in real time according to the initial ESR and the real-time ESR, and the purpose of estimating the health state of the electrolytic capacitor on line independent of a system structure is achieved.
Claims (10)
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| CN110470934B (en) * | 2019-09-02 | 2022-04-29 | 重庆中涪科瑞工业技术研究院有限公司 | Traction transmission system direct current side support capacitance state monitoring circuit and method |
| CN112542841B (en) * | 2020-11-19 | 2022-04-22 | 国网湖北省电力有限公司电力科学研究院 | A method for real-time monitoring of the life of DC side electrolytic capacitors of active power filters |
| CN112198390B (en) * | 2020-12-03 | 2021-04-02 | 广东电网有限责任公司佛山供电局 | Real-time evaluation method and system for health state of capacitor bank |
| CN113437867B (en) * | 2021-08-03 | 2022-06-17 | 陕西理工大学 | Intrinsic safety Buck converter parameter design method considering temperature effect |
| CN114200206B (en) * | 2021-12-07 | 2023-02-10 | 嘉兴丹那赫电子科技有限公司 | Frequency converter convenient to monitor and monitoring method thereof |
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