CN111812409A - Online estimation method of ESR (equivalent series resistance) of direct current capacitor - Google Patents

Online estimation method of ESR (equivalent series resistance) of direct current capacitor Download PDF

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CN111812409A
CN111812409A CN202010505659.8A CN202010505659A CN111812409A CN 111812409 A CN111812409 A CN 111812409A CN 202010505659 A CN202010505659 A CN 202010505659A CN 111812409 A CN111812409 A CN 111812409A
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capacitor
res
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向大为
郑燕
李豪
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Tongji University
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    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
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    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
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Abstract

The invention relates to an online estimation method of a direct current capacitor ESR, which comprises the following steps: 1) detecting initial value R of total resistance of loop of converter systemres0And the capacitance C of the absorption capacitors(ii) a 2) Intercepting DC capacitor current high-frequency oscillation signal Ssw_res(t) the kth high-frequency oscillation section Ssw_res(k) (ii) a 3) Method for acquiring high-frequency oscillation signal segment S by adopting half-power methodsw_res(k) The oscillation damping ratio and the resonance frequency of (c); 4) calculating the resistance R of the resonant tankres(ii) a 5) Calculating the ESR variation DeltaESRCdcI.e. an on-line estimate of the dc capacitance ESR. Compared with the prior art, the method has the advantages of high accuracy, easiness in implementation, interference reduction and the like.

Description

Online estimation method of ESR (equivalent series resistance) of direct current capacitor
Technical Field
The invention relates to the field of direct current capacitor monitoring, in particular to an online estimation method of a direct current capacitor ESR.
Background
The direct current capacitor has filtering, energy storage and input and output isolation functions in the converter, and is widely applied to important fields of power grids, photovoltaics, new energy automobiles and the like. Particularly, a direct current capacitor in a high-power system has large working current, high power and serious heating, and is one of the most easily-degraded components in the converter, so that the monitoring of the state of the direct current capacitor has important significance on the safe and reliable operation of the converter system.
The health status of the dc capacitor is generally judged by two indicators: capacity value and series equivalent resistance ESR, taking electrolytic capacitor as an example, when the capacity value is reduced by 20%,The capacitor failure can be judged by increasing ESR by 100-200%. The state of health of an electrolytic capacitor is generally monitored by ESR, using the capacitor PWM voltage ripple DeltauhAnd current ripple Δ ihEstimate ESR ═ Δ uh/ΔihHowever, the PWM ripple voltage and current amplitude are very small and constantly change with the operating condition, and are difficult to accurately detect.
Chinese patent 202010070754.X proposes a system and method for obtaining ESR information of a dc capacitor on-line by detecting a high-frequency oscillation damping characteristic of a dc capacitor switch of a converter, the method is not affected by a signal amplitude, an error caused by a change in a working condition can be avoided, robustness is high, the patent obtains the damping characteristic of the switching oscillation by a time-domain fitting method, but signals with dynamic dc components and other frequency components are also mixed in a switching oscillation signal in an actual system, and interference is caused to accurate extraction of damping characteristic parameters.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an online estimation method of a direct current capacitor ESR, which is used for acquiring high-frequency oscillation damping information in a frequency domain based on a half-power method to realize online monitoring of the ESR of the direct current capacitor, so that the influence of other frequency signal components is avoided.
The purpose of the invention can be realized by the following technical scheme:
an online estimation method of a direct current capacitor ESR comprises the following steps:
1) detecting initial value R of total resistance of loop of converter systemres0And the capacitance C of the absorption capacitors；
2) Intercepting DC capacitor current high-frequency oscillation signal Ssw_res(t) the kth high-frequency oscillation section Ssw_res(k)；
3) Method for acquiring high-frequency oscillation signal segment S by adopting half-power methodsw_res(k) The oscillation damping ratio and the resonance frequency of (c);
4) calculating the resistance R of the resonant tankres；
5) Calculating the ESR variation DeltaESRCdcI.e. on-line estimation of the dc capacitance ESR。
In the step 1), the initial value R of the total loop resistance of the converter system is detected in an online or offline moderes0And the capacitance C of the absorption capacitors。
In the step 1), the absorption capacitor in the converter system is a thin film capacitor.
In the step 3), the oscillation damping ratio zeta is defined as the ratio of the bandwidth of the damped oscillation half-power area to the resonant frequency, and the damped oscillation half-power area is defined as being distributed in a frequency spectrum
Figure BDA0002526450250000021
The area within the peak.
The expression of the oscillation damping ratio ζ is:
ζ＝(f2-f1)/f0
wherein f is1、f2Is a half power point, f2-f1Is the bandwidth of half power region, f0Is the resonant frequency.
In the step 4), the resistance R of the resonant circuitresThe calculation formula of (A) is as follows:
Rres＝ζ/(πCsf0)。
in the step 5), the ESR variation Δ ESRCdcThe calculation formula of (A) is as follows:
ΔESRCdc＝Rres-Rres0。
in the step 5), in order to avoid accidental errors, the resistance R of the resonant circuit corresponding to each high-frequency oscillation signal segment is respectively calculatedres(k) The average value is obtained as the final resonant circuit resistance R in the range corresponding to the variation of the capacitance ESRres。
The range of the ESR variation of the coincidence capacitor is 1-5 times.
In the step 2), the current high-frequency oscillation signal S of the direct current capacitorsw_resThe expression of (t) is:
Figure BDA0002526450250000022
wherein, ω isnIs the natural oscillation frequency and t is time.
Compared with the prior art, the invention has the following advantages:
firstly, the accuracy is high: according to the invention, a half-power method is adopted to obtain a large amount of information of a frequency band near the resonant frequency, so that the detection precision of the resonant frequency and the damping characteristic parameter is effectively improved, and the accurate estimation of the ESR variation of the direct current capacitor is realized.
Secondly, interference is reduced: the existing estimation method adopts a time domain method to extract damping parameters of high-frequency oscillation, is easily interfered by low-frequency oscillation, adopts a frequency domain method to obtain the damping parameters of the high-frequency oscillation only by using data near resonant frequency, is not influenced by the low-frequency oscillation, and improves the accuracy.
Thirdly, the implementation is easy: the half-power method of the invention adopts FFT algorithm without iterative cycle, and is easy to realize engineering.
Drawings
Fig. 1 shows a dc capacitor high frequency oscillating circuit of a current transformer.
Fig. 2 is a flowchart of a method for extracting ESR variation of a dc capacitor by using a half-power method.
Fig. 3 shows the principle of obtaining the damping ratio by the half-power method.
Fig. 4 is a high frequency oscillation waveform.
Fig. 5 is a measured waveform of the PWM high-frequency oscillation current of the dc capacitor bank under different ESR conditions.
Fig. 6 shows the per-unit amplitude-frequency characteristics of the switching high-frequency oscillation under different ESR conditions.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
The invention provides a method for extracting damping characteristic parameters (including damping ratio and resonant frequency) of a high-frequency oscillation signal of a direct current capacitor switch by using a half-power method according to the characteristics of high-frequency oscillation of the converter switch, so as to realize online accurate estimation of the ESR of the direct current capacitor.
The invention provides a method for extracting an ESR (equivalent series resistance) change value of a direct current capacitor based on a half-power method by utilizing voltage high-frequency oscillation and current high-frequency oscillation between a direct current capacitor at the direct current side and an absorption capacitor parallel loop when a converter works, and as shown in figure 2, the specific implementation steps comprise the following flows:
1) initialization: initial value R of total resistance of off-line or on-line detection system loopres0And the capacitance C of the absorption capacitors. The absorption capacitance is a film capacitance, the working power is low, the cracking probability is low relative to an electrolytic capacitor, and the capacitance value after absorption cracking is changed by about 2 percent and can be almost ignored, and C is considered to besHardly changes;
2) intercepting an oscillation fragment: the high-frequency oscillation signal will be attenuated to 0 in ten or more mus after the power electronic switch is operated, the high-frequency oscillation S of the current of the DC capacitorSW_resContains a large amount of useless data, and only needs to extract the oscillation part signal SSW_res(k) Processing is carried out, the redundancy of data is reduced, and the efficiency is improved;
3) the half-power method extracts the damping ratio and the frequency: the high frequency oscillation damping signal spectrum is typically distributed over a certain area centered at the resonance frequency, as shown in fig. 3. Qualitatively, the wider the frequency spectrum distribution of the oscillation signal, the larger the energy dispersion and damping; quantitatively, the distribution is defined in the frequency spectrum
Figure BDA0002526450250000041
The area in the peak value is a damping oscillation half-power area, as shown in formula (1), the oscillation damping ratio is equal to the ratio of the bandwidth of the half-power area to the resonant frequency;
ζ＝(f2-f1)/f0(1)
4) calculating the resistance R of the resonant tankres: the high-frequency oscillation segment and the expression thereof are shown in FIG. 4, the high-frequency oscillation decays exponentially, the oscillation damping ratio ζ represents the decay rate of the high-frequency oscillation, and the known absorption capacitance CsAnd obtaining the oscillation damping ratio zeta and the resonant frequency f by a half-power method0The loop resistance R can be obtained from the formula (2)res：
Figure BDA0002526450250000042
5) Calculating the ESR variation DeltaESRCdc: to avoid accidental errors, R corresponding to each segment is calculated separatelyresValue, R is obtained within a certain range (1-5 times range)resIf the average value of (1) is out of range, the calculation error is determined to be discarded, and the initial R is subtractedres0The variation value Delta ESR of the DC capacitor can be obtainedCdc＝Rres-Rres0。
Examples
In the embodiment, a 380V/7.5kW induction motor variable frequency speed control system is used as an example, and the structure is shown in figure 1. When the induction motor works normally, the direct current power supply drives the induction motor to work through the converter, and specific parameters are shown in table 1.
TABLE 1 simulation model parameters of variable frequency speed control system of induction motor
Rated power of motor 7.5kW DC capacitor bank Cdc 1500μF
Rated voltage of motor 380V DC supply voltage 600V
Rated frequency of motor 50Hz Absorption capacitance Cs 0.47μF
High-frequency oscillation current i of converter direct-current capacitorSW_resAs shown in FIG. 5, wherein iaIs the motor line current. The high-frequency oscillation frequency is about 495kHz, the decay time is about 15 mu s, the capacitance value of a direct current capacitor is far larger than that of an absorption capacitor, the capacitance determining the high-frequency oscillation performance is mainly the absorption capacitor, in order to simulate the change of the ESR2 of the direct current capacitor, the embodiment adopts capacitor banks with different connection modes, wherein the ESR of two series of the direct current capacitor banks in parallel is 28m omega, the ESR of two series of the direct current capacitor banks in parallel is 41m omega, the ESR of two series of the direct current capacitor banks in parallel is 82m omega, and the decay of the envelope curve of the capacitor banks along with the increase of the ES.
The high-frequency oscillation waveform of fig. 5 is subjected to FFT to obtain the amplitude-frequency characteristic, the larger the damping is, the larger the energy dispersion of the amplitude-frequency characteristic with respect to the center frequency is, and finally, the ESR result is calculated as shown in table 2, which is substantially consistent with the measured value, and the error is less than 1m Ω, thus it can be seen that the algorithm provided by the present invention has high accuracy.
TABLE 2 DC CAPACITOR GROUP ESR ON-LINE MONITORING EXPERIMENTAL RESULT
Figure BDA0002526450250000043
Figure BDA0002526450250000051

Claims (10)

1. An online estimation method for ESR (equivalent series resistance) of a direct current capacitor is characterized by comprising the following steps:
1) detecting initial value R of total resistance of loop of converter systemres0And the capacitance C of the absorption capacitors；
2) Intercepting DC capacitor current high-frequency oscillation signal Ssw_res(t) the kth high-frequency oscillation section Ssw_res(k)；
3) Method for acquiring high-frequency oscillation signal segment S by adopting half-power methodsw_res(k) The oscillation damping ratio and the resonance frequency of (c);
4) calculating the resistance R of the resonant tankres；
5) Calculating the ESR variation DeltaESRCdcI.e. an on-line estimate of the dc capacitance ESR.
2. The method for online estimation of ESR as claimed in claim 1, wherein in step 1), the initial value R of the total loop resistance of the converter system is detected online or offlineres0And the capacitance C of the absorption capacitors。
3. The method for online estimation of ESR of claim 1, wherein in step 1), the absorption capacitor in the converter system is a film capacitor.
4. The method as claimed in claim 1, wherein in the step 3), the oscillation damping ratio ζ is defined as a ratio of a bandwidth of a half-power region of the damped oscillation to a resonant frequency, and the half-power region of the damped oscillation is defined as being distributed in a frequency spectrum
Figure FDA0002526450240000011
The area within the peak.
5. The method for on-line estimation of ESR as recited in claim 4, wherein the oscillation damping ratio ζ is expressed as:
ζ＝(f2-f1)/f0
wherein f is1、f2Is a half power point, f2-f1Is the bandwidth of half power region, f0Is the resonant frequency.
6. The method for online estimation of ESR of DC capacitor as claimed in claim 5, wherein in step 4), the R resistance of the resonant tank is measuredresThe calculation formula of (A) is as follows:
Rres＝ζ/(πCsf0)。
7. the method for online estimation of ESR of DC capacitor as claimed in claim 5, wherein in the step 5), the ESR variation Δ ESR is determinedCdcThe calculation formula of (A) is as follows:
ΔESRCdc＝Rres-Rres0。
8. the method for online estimating ESR as recited in claim 7, wherein in the step 5), for avoiding accidental errors, the resistance R of the resonant tank corresponding to each high frequency oscillation signal segment is calculated separatelyres(k) The average value is obtained as the final resonant circuit resistance R in the range corresponding to the variation of the capacitance ESRres。
9. The method for on-line estimation of ESR of DC capacitor as claimed in claim 8, wherein the ESR variation of the said coincidence capacitor is in the range of 1-5 times.
10. The method for online estimation of ESR of DC capacitor as claimed in claim 1, wherein in step 2), the DC capacitor current high frequency oscillation signal Ssw_resThe expression of (t) is:
Figure FDA0002526450240000021
wherein, ω isnIs the natural oscillation frequency and t is time.
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CN112698142A (en) * 2021-01-26 2021-04-23 哈尔滨工业大学 Method for identifying failure parameters of electrolytic capacitor in direct current converter
CN115047214A (en) * 2022-03-17 2022-09-13 中国科学院地质与地球物理研究所 Detection method and device for MEMS acceleration sensor chip

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