CN112433097B - Film capacitor ESL extraction method based on switch transient frequency information - Google Patents

Film capacitor ESL extraction method based on switch transient frequency information Download PDF

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CN112433097B
CN112433097B CN202011229111.1A CN202011229111A CN112433097B CN 112433097 B CN112433097 B CN 112433097B CN 202011229111 A CN202011229111 A CN 202011229111A CN 112433097 B CN112433097 B CN 112433097B
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capacitor
silicon carbide
esl
carbide mosfet
film capacitor
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CN112433097A (en
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胡斯登
王明阳
梁梓鹏
何湘宁
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Zhejiang University ZJU
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G01R23/16—Spectrum analysis; Fourier analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere

Abstract

The invention discloses a thin film capacitor ESL extraction method based on switching transient frequency information, which is carried out according to the following steps: a. constructing a silicon carbide MOSFET double-pulse test platform; the capacitor to be tested is used as the bus capacitance of the silicon carbide MOSFET double-pulse test platform and is embedded into a laminated bus bar with known parasitic parameters; b. measuring the voltage waveform of the switching-on or switching-off transient state of the silicon carbide MOSFET, and extracting the voltage under-damped oscillation frequency excited by a loop between a capacitor to be tested and the parasitic capacitor of the laminated busbar by utilizing Fourier transform; c. and calculating the internal ESL of the capacitor to be measured according to the measured voltage under-damped oscillation frequency. The silicon carbide MOSFET double-pulse test platform has the advantages of low cost and miniaturization, avoids large-current oscillation of the capacitor body in the ESL extraction process, does not need additional short-circuit test, and has high test safety.

Description

Film capacitor ESL extraction method based on switch transient frequency information
Technical Field
The invention relates to the technical field of power electronic testing, in particular to a thin film capacitor ESL extraction method based on switching transient frequency information.
Background
Compared with an electrolytic capacitor, the metallized film capacitor has longer service life and higher long-term operation reliability, is used as a direct current bus support capacitor, and is widely applied to high-capacity power electronic devices such as flexible direct current transmission systems, traffic traction systems and the like. The method is limited by a production process, equivalent series inductance (ESL) inside the film capacitor cannot be ignored and is used as one of main components of stray inductance of a converter loop of a support capacitor-power device, voltage overshoot and loss of a power device switch transient state are increased, and design margin of a converter is restricted; in addition, the internal ESL of the film capacitor improves the resonance risk of stray inductance and capacitance of the power loop, so that the current ripple of the supporting capacitor is increased, and the heat damage probability of the capacitance and the connecting piece of the capacitance is increased. Therefore, accurate extraction of the internal ESL of the film capacitor is a key step for judging whether the capacitor production process reaches the standard, and quantitative analysis of the operation reliability of the power electronic converter is facilitated.
Because an accurate ESL measuring method is not provided, the data manual of the existing film capacitor only provides an approximate range of ESL, and the capacitor operates at different power levels for a long time, so that the difference of the ESL among the film capacitors after use exists, and the reference of the data manual is low. The traditional measurement method comprises the step of directly measuring by using a high-precision LCR meter or an impedance analyzer, however, the reliability of the extraction result is low because the capacitance value of the film capacitor is difficult to keep stable under the measurement voltage of a signal level, and the accuracy is influenced by various factors such as a probe clamp, excitation frequency and the like. The experimental method for indirectly extracting the ESL effectively avoids the problems by applying power voltage at two ends of the thin-film capacitor and measuring the voltage and current oscillation waveform of the capacitor discharge transient state, and gradually becomes the mainstream method for extracting the ESL of the thin-film capacitor.
The patent with the publication number of CN108646098A provides an experimental method for detecting the ESL in the self-healing metallized film capacitor based on the ESL measuring method in the standard JB/T8168-1999; this measurement method has certain drawbacks and limitations: (1) the oscillation current is excited by the thin film capacitor body, the peak value of the discharge current reaches the kA level, the test condition is relatively dangerous, and the measurement is difficult to be used for measuring the ESL of the thin film capacitor at the end of the life cycle; (2) the additional inductance of the measuring loop is difficult to completely eliminate, and even if a short-circuit experiment is adopted to avoid errors, the extra stray inductance introduced by the used short-circuit connecting piece is still difficult to determine; (3) the test equipment comprises a high-range current transformer and a capacitor discharge circuit, so that the test platform is relatively heavy and high in cost.
Disclosure of Invention
The invention aims to provide a thin film capacitor ESL extraction method based on switching transient frequency information. The silicon carbide MOSFET double-pulse test platform has the advantages of low cost and miniaturization, avoids large-current oscillation of the capacitor body in the ESL extraction process, and improves the test safety; in addition, the laminated busbar with known parasitic parameters is used as a carrier of the capacitor to be measured, and all additional inductance can be almost eliminated without extra short-circuit experiments.
The technical scheme of the invention is as follows: a thin film capacitor ESL extraction method based on switching transient frequency information is carried out according to the following steps:
a. constructing a silicon carbide MOSFET double-pulse test platform; the silicon carbide MOSFET double-pulse test platform comprises a capacitor to be tested, a laminated bus bar, a silicon carbide Schottky barrier diode and a silicon carbide MOSFET which are sequentially connected in series, wherein load inductors are connected in parallel at two ends of the silicon carbide Schottky barrier diode; the capacitor to be tested is used as the bus capacitance of the silicon carbide MOSFET double-pulse test platform and is embedded into a laminated bus bar with known parasitic parameters;
b. detecting and collecting the on-state or off-state transient voltage waveform of the silicon carbide MOSFET through a voltage probe and an oscilloscope, extracting the voltage under-damped oscillation frequency excited by a loop between a capacitor to be detected and a parasitic capacitor of the laminated busbar by utilizing Fourier transform, and recording the frequency as f1；
c. Underdamped frequency of oscillation f of the voltage measured according to step b1The internal ESL of the capacitor to be measured is calculated as LESL；
Figure BDA0002764570120000031
Wherein L is1And C1The parameters are known as the stray inductance and the stray capacitance of the laminated busbar respectively.
In the thin film capacitor ESL extraction method based on switching transient frequency information, the switching-on or switching-off process of the laminated busbar in the silicon carbide MOSFET is characterized by one-half stray inductance L1/2 parasitic capacitance C1And half stray inductance L1T-type equivalent circuit model of/2.
In the aforementioned method for extracting ESL of thin film capacitor based on switching transient frequency information, in step c, the stray inductance L of the laminated busbar1And parasitic capacitance C1By means of finite element-based numerical algorithm, surface element numerical valueAnd extracting by using numerical simulation software of the algorithm or the PEEC numerical algorithm.
In the aforementioned method for extracting ESL of thin film capacitor based on switching transient frequency information, in step c, the stray inductance L of the laminated busbar1And parasitic capacitance C1The extraction is performed by an LCR meter, an impedance analyzer or a network analyzer.
Compared with the prior art, the method has the advantages that the silicon carbide MOSFET double-pulse test platform is built, the voltage under-damped oscillation frequency excited by a loop between the capacitor to be tested and the parasitic capacitor of the laminated busbar in the process of switching on or switching off the silicon carbide MOSFET is measured, and the extraction of the ESL in the capacitor to be tested is indirectly realized. Compared with an ESL extraction method utilizing a large-current oscillation waveform of a thin-film capacitor body, the under-damped oscillation excited by the method is derived from electromagnetic energy exchange between stray inductance and parasitic capacitance of the laminated busbar, the current level is low, and potential safety hazards in a testing link are avoided; the invention adopts the laminated busbar with known parasitic parameters as the carrier of the capacitor to be measured, does not need to adopt an extra short-circuit experiment to avoid the extraction error caused by additional inductance, and has simple and convenient measurement and data processing flows; the silicon carbide power device double-pulse circuit is used as a test platform, and only a voltage probe is needed to measure the on-state or off-state transient voltage waveform of the silicon carbide MOSFET, so that the low cost and miniaturization of test equipment are guaranteed.
Drawings
FIG. 1 is a schematic diagram of a silicon carbide MOSFET double pulse test platform in accordance with the present invention.
FIG. 2 shows a new thin film capacitor V according to an embodiment of the present inventionds1The test waveform of (2).
FIG. 3 shows a view of V in an embodiment of the present inventionds1Fast fourier analysis of the frequency map.
FIG. 4 shows an old thin film capacitor V in an embodiment of the present inventionds2The test waveform of (2).
FIG. 5 shows a view of V in an embodiment of the present inventionds2Fast fourier analysis of the frequency map.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
Example 1: a method for extracting ESL of a film capacitor based on switching transient frequency information comprises the following steps:
a. constructing a silicon carbide MOSFET double-pulse test platform; as shown in fig. 1, the silicon carbide MOSFET double-pulse test platform comprises a capacitor to be tested, a laminated busbar, a silicon carbide schottky barrier diode and a silicon carbide MOSFET which are sequentially connected in series, wherein load inductances are connected in parallel at two ends of the silicon carbide schottky barrier diode, and the capacitor to be tested is represented as CtThe silicon carbide schottky barrier diode is denoted as D, the silicon carbide MOSFET is denoted as S, and the load capacitance is denoted as Lload(ii) a The capacitor to be tested is used as a bus capacitor of the silicon carbide MOSFET double-pulse test platform and is embedded into a laminated bus bar with known parasitic parameters; the geometric structure of the laminated busbar and the interface size of the capacitor to be measured need to be customized according to the actual size of the capacitor to be measured.
In the silicon carbide MOSFET double-pulse test platform, two poles of a capacitor to be tested are respectively connected with a positive laminated busbar and a negative laminated busbar; the cathode of the silicon carbide Schottky barrier diode is connected with the output port of the positive laminated busbar, and the source of the silicon carbide MOSFET is connected with the output port of the negative laminated busbar; the anode of the silicon carbide Schottky barrier diode is connected with the drain electrode of the silicon carbide MOSFET, and the gate level of the silicon carbide MOSFET is connected with the driving circuit.
As shown in fig. 1, the stray inductance and the stray capacitance of the laminated busbar are respectively represented as L1 and C1By one-half stray inductance L during switching of the silicon carbide MOSFET1/2 parasitic capacitance C1And half stray inductance L1A T-shaped equivalent circuit model representation of/2; the total stray inductance of the silicon carbide Schottky barrier diode and the silicon carbide MOSFET bridge arm loop is expressed as L2。
The silicon carbide MOSFET double-pulse test platform comprises two oscillation circuits, wherein a parasitic capacitor of the laminated busbar and a silicon carbide MOSFET bridge arm form a high-frequency oscillation circuit, and the under-damped oscillation is realized by stray inductance L2+L1The/2 is excited together with the junction capacitance of the silicon carbide MOSFET and belongs to a useless frequency in the test(ii) a The capacitor to be tested and the parasitic capacitance of the laminated busbar form a low-frequency oscillation loop, and the under-damped oscillation is realized by stray inductance LESL+L1And/2, the frequency is excited together with the parasitic capacitance of the laminated busbar and is the frequency required to be extracted in the test process.
In the silicon carbide MOSFET double-pulse test platform, the silicon carbide Schottky barrier diode and the silicon carbide MOSFET adopt matched products with similar power levels, and a driving signal is provided for the silicon carbide MOSFET through the isolation driving chip; the test conditions of the silicon carbide MOSFET double-pulse test platform are selected as follows: the bus voltage is 400V-800V, the tested load current is 10-20A, and the driving resistance is 5-15 ohm. The selection principle of the test condition is to adopt higher test voltage, current and smaller driving resistance as far as possible on the premise of ensuring the reliable work of the silicon carbide MOSFET, thereby increasing the under-damped oscillation amplitude of the voltage.
b. In the double-pulse test of the silicon carbide MOSFET, two voltage isolation probes are adopted to be matched with a multi-channel oscilloscope to respectively measure the gate-level voltage V of the silicon carbide MOSFETgsAs a trigger signal, and the drain-source voltage V of the silicon carbide MOSFETdsThe waveform is processed as subsequent data.
Extracting V by fast Fourier transformdsThe frequency of the voltage underdamped oscillation excited by the loop between the capacitor to be measured and the parasitic capacitance of the laminated busbar is denoted as f1(ii) a The voltage waveform is intercepted for a sufficient time length during the test, so as to improve the accuracy of the mathematical analysis of the voltage waveform.
c. Underdamped frequency of oscillation f of the voltage measured according to step b1The internal ESL of the capacitor to be measured is calculated as LESL；
Figure BDA0002764570120000061
Wherein, the stray inductance L of the laminated busbar1And parasitic capacitance C1Extracting by numerical simulation software based on finite element numerical algorithm, surface element numerical algorithm or PEEC numerical algorithmThe extraction may be performed by an LCR meter, an impedance analyzer, or a network analyzer.
Example 2: based on embodiment 1, as a specific example, two old and new metalized film capacitors are selected as the capacitor to be tested, wherein the new film capacitor is represented as CtNAnd LESLNEquivalent series model of (1), old film capacitor is denoted as CtOAnd LESLOThe equivalent series model of (1).
Taking the turn-off transient voltage of the silicon carbide MOSFET in the double-pulse test platform as an example, when the new film capacitor is used as the bus capacitor, the turn-off voltage waveform of the silicon carbide MOSFET is recorded as Vds1And the turn-off voltage waveform when the old film capacitor is used as the bus capacitor is recorded as Vds2；Vds1The waveform is shown in FIG. 2, Vds2The waveform is shown in fig. 4.
According to the measured turn-off voltage waveform, respectively for Vds1And Vds2And performing fast Fourier transform. Vds1Is shown in FIG. 3, Vds2Is shown in fig. 5. As can be observed from fig. 3 and 5, each turn-off voltage waveform has two distinct peak frequencies, corresponding to the under-damped oscillation frequency of each loop, where only low-frequency oscillation excited by the parasitic capacitance loop of the thin film capacitor-laminated busbar to be tested is concerned. Recording the peak frequencies of two low-frequency oscillations in the spectrogram, where Vds1The low frequency oscillation frequency of (2) is 16.5MHz, and is marked as fN；Vds2The low frequency oscillation frequency of (2) is 18.0MHz, and is marked as fO。
In this embodiment, the stray parameters of the laminated busbar are extracted by using ANSYS Q3D electromagnetic numerical simulation software, the extraction section of the stray inductance is the output port of the power device from the support capacitor port to the laminated busbar, and the extracted stray inductance L is16.2nH, parasitic capacitance C1The extraction result of (2) was 2.8 nH.
Finally, the extraction of the ESL of the new film capacitor and the old film capacitor can be realized by solving the following equation.
Figure BDA0002764570120000081
Figure BDA0002764570120000082
The extraction result is as follows: ESL size L of novel thin film capacitorESLN30.1nH, ESL size L of old film capacitorESLO24.8 nH; as can be known from a data manual of the thin film capacitor, the size of the ESL in the thin film capacitor is within 50nH, and a test result is within a reasonable range; in addition, according to the use experience, the ESL of the film capacitor is gradually reduced along with the aging of the use, and the test result is in accordance with the empirical analysis.
In conclusion, the silicon carbide MOSFET double-pulse test platform constructed by the invention has the advantages of low cost and miniaturization, avoids large-current oscillation of the capacitor body in the extraction process, and improves the test safety; in addition, the laminated busbar with known parasitic parameters is used as a carrier of the capacitor to be measured, and all additional inductance can be almost eliminated without extra short-circuit experiments.

Claims (3)

1. A thin film capacitor ESL extraction method based on switch transient frequency information is characterized in that: the method comprises the following steps:
a. constructing a silicon carbide MOSFET double-pulse test platform; the silicon carbide MOSFET double-pulse test platform comprises a capacitor to be tested, a laminated bus bar, a silicon carbide Schottky barrier diode and a silicon carbide MOSFET which are sequentially connected in series, wherein load inductors are connected in parallel at two ends of the silicon carbide Schottky barrier diode; the capacitor to be tested is used as the bus capacitance of the silicon carbide MOSFET double-pulse test platform and is embedded into a laminated bus bar with known parasitic parameters;
b. detecting and collecting the on-state or off-state transient voltage waveform of the silicon carbide MOSFET through a voltage probe and an oscilloscope, extracting the voltage under-damped oscillation frequency excited by a loop between a capacitor to be detected and a parasitic capacitor of the laminated busbar by utilizing Fourier transform, and recording the frequency as f1；
c. Underdamped frequency of oscillation f of the voltage measured according to step b1Calculating the capacitor to be measured according to the following formulaInternal ESL of (2), noted as LESL；
Figure FDA0003158865320000011
Wherein L is1And C1The parameters are known as the stray inductance and the stray capacitance of the laminated busbar respectively.
2. The ESL extraction method for the film capacitor based on the switching transient frequency information as claimed in claim 1, wherein: the laminated busbar stray inductance L in the step c1And parasitic capacitance C1Extracting through numerical simulation software based on a finite element numerical algorithm, a surface element numerical algorithm or a PEEC numerical algorithm.
3. The ESL extraction method for the film capacitor based on the switching transient frequency information as claimed in claim 1, wherein: the laminated busbar stray inductance L in the step c1And parasitic capacitance C1The extraction is performed by an LCR meter, an impedance analyzer or a network analyzer.
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