Emi modeling and spectral analysis method for si / sic hybrid devices

Abstract

The application belongs to the technical field of power electronics, and relates to an EMI modeling and spectrum analysis method for Si / SiC hybrid devices, which comprises the following steps: S1: according to the actual switching process of the hybrid device, reasonably simplifying the common-mode voltage waveform, and constructing an asymmetric trapezoidal wave capable of reflecting the rising edge, the falling edge and the conduction stage; S2: constructing a segmented mathematical function expression, performing Fourier transform on the segmented mathematical function expression, and obtaining an n-th harmonic amplitude expression of the common-mode voltage; S3: according to the different frequency bands, taking the envelope of the harmonic amplitude, obtaining a four-segment spectrum peak envelope expression, and determining the turning frequencies between the segments; and S4: analyzing the influence law of the bus voltage, the rise time, the fall time and the switching time sequence on the spectrum peak, and using the influence law to guide the EMI optimization design. According to the method, the interference amplitudes under different harmonic numbers can be quickly predicted without relying on time domain simulation, and the analysis efficiency of the EMI characteristics is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to an EMI modeling and spectrum analysis method for Si / SiC hybrid devices. Background Technology

[0002] Si / SiC hybrid devices combine the high current handling capability of Si IGBTs with the low switching losses of SiC MOSFETs, meeting the requirements of high-efficiency, high-power-density power electronic converters. However, during actual switching, the high switching speed and high-frequency switching characteristics of SiC MOSFETs result in extremely high dv / dt and di / dt change rates, leading to severe EMI (electromagnetic interference) problems. In particular, the rapid transition of the common-mode voltage VDS can generate common-mode current through parasitic capacitance coupling, seriously threatening the system's electromagnetic compatibility. Therefore, a thorough understanding of the EMI generation mechanism during the switching process of Si / SiC hybrid devices and the establishment of an accurate and analytical EMI model are of significant theoretical and engineering importance for guiding their electromagnetic compatibility design and reliable application.

[0003] Currently, EMI modeling research for power devices mainly focuses on single-type Si or SiC devices, whose common-mode voltage waveforms are often simplified to symmetrical trapezoidal waves for frequency domain analysis. However, Si / SiC hybrid devices exhibit unique switching behavior: on the one hand, the switching timing of SiC MOSFETs and Si IGBTs differs, such as SiC MOSFETs turning on first and then off, while SiIGBTs turn on later and then off first, resulting in a significant asymmetric VDS waveform; on the other hand, parameters such as the conduction ratio and switching time of hybrid devices can be dynamically adjusted to adapt to different operating conditions, allowing the rising and falling edges of the VDS waveform to vary independently. Existing models generally employ fixed or symmetrical waveform assumptions, which cannot effectively describe the aforementioned asymmetric and variable VDS characteristics, and lack systematic analytical analysis of the impact of control variables specific to hybrid devices, such as switching timing, on the EMI spectrum peak value. Summary of the Invention

[0004] To address the aforementioned technological gaps, this invention proposes an EMI modeling and spectrum analysis method for Si / SiC hybrid devices. This modeling method has the following characteristics: 1) It considers the asymmetry of the rising and falling edges of the common-mode voltage VDS, accurately describing the voltage waveform and spectrum characteristics; 2) Based on the proposed expression, it analyzes the influence of switching timing and bus voltage on the EMI spectrum peak value. The research results demonstrate that interference amplitudes at different harmonic orders can be quickly predicted without relying on time-domain simulation, significantly improving the efficiency of EMI characteristic analysis. Simultaneously, it provides guidance for optimizing parameters such as drive resistor adjustment and switching timing, ultimately achieving thermal equilibrium and low EMI.

[0005] The technical solution adopted in this invention is an EMI modeling and spectrum analysis method for Si / SiC hybrid devices, which includes the following steps: S1: Based on the actual switching process of hybrid devices, the common-mode voltage waveform is reasonably simplified to construct an asymmetric trapezoidal wave that can reflect the rising edge, falling edge and conduction stage; S2: Construct a piecewise mathematical function expression based on the asymmetric trapezoidal wave, and perform a Fourier transform on the piecewise mathematical function expression to obtain the nth harmonic amplitude expression of the common-mode voltage; S3: Take the envelope of the harmonic amplitude according to different frequency bands to obtain the four-segment spectrum peak envelope expression, and determine the corner frequencies between each segment; S4: Based on the envelope expression, analyze the influence of bus voltage, rise time, fall time and switching sequence on the peak value of the spectrum, so as to guide EMI optimization design.

[0006] Furthermore, the reasonable simplification in S1 specifically includes: ignoring voltage overshoot during the turn-off process, assuming that the rate of change of common-mode voltage is constant during the turn-on and turn-off processes, and assuming that the voltage rise time and fall time are different.

[0007] Furthermore, the piecewise mathematical function expression of the asymmetric trapezoidal wave is: ; In the formula, This refers to the bus voltage across the device. and These represent the rise time and the fall time, respectively. The time taken from half the rise to half the fall. The period of the asymmetric trapezoidal wave pulse.

[0008] Furthermore, the amplitude of the nth harmonic The expression is: ; in: ; ; ; In the formula, , These are the harmonic frequency and the switching frequency, respectively.

[0009] Furthermore, the expression for the four-segment spectral peak envelope in S3 is as follows: High frequency band: ; Mid-to-high frequency band: ; Mid-to-low frequency band: ; Low frequency band: ; The transition frequency is: .

[0010] Furthermore, the switching timing in S4 includes four modes: Switching timing A: MOSFET is turned on first and then turned off; Switching sequence B: IGBT is turned on first and then turned off; Switching timing C: All switches are turned on simultaneously, and the MOSFETs are turned off later. Switching sequence D: Simultaneous on and simultaneous off; By analyzing different time series and The changes in these parameters are used to predict the trend of EMI spectrum peak values.

[0011] Furthermore, the rise time of switching timing A and switching timing C. and descent time The harmonic frequency is smaller, and the high-frequency components in the middle and high-frequency bands increase; Rise time in switch sequence B and descent time The harmonic frequency is relatively large, and the high-frequency components in the middle and high-frequency bands are reduced; The increase or decrease of the D harmonic frequency component in the switching timing needs to be based on and Detailed analysis.

[0012] Furthermore, the S4 bus voltage only affects the harmonic amplitude and does not change the corner frequency; reduce or This will increase the amplitude of the high-frequency or mid-high-frequency harmonics and increase the corresponding turnaround frequency.

[0013] The beneficial effects of this invention are: (1) Based on the asymmetric trapezoidal wave piecewise function established in this invention, analytical expressions for the nth harmonic of the VDS waveform and the peak value of the EMI spectrum are derived. This expression establishes a direct mathematical relationship between the switching parameters of the hybrid device (such as rise / fall time, VDS, etc.) and the common-mode interference spectrum, which can quickly predict the interference amplitude under different harmonic orders without relying on time-domain simulation, thus significantly improving the analysis efficiency of EMI characteristics.

[0014] (2) The present invention systematically analyzes the influence of various parameters on EMI, including different switching sequences and the switching time of hybrid devices, which can provide guidance for the coordinated design of thermal balance and low EMI, such as driving resistor adjustment and switching sequence. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a Si / SiC hybrid device; Figure 2 These are transient waveforms during the turn-on and turn-off processes of a Si / SiC hybrid device; where (a) is the turn-on process and (b) is the turn-off process. Figure 3 It is an asymmetric trapezoidal wave; Figure 4 It is the peak value of the EMI spectrum; Figure 5 The effect of bus voltage variation on EMI spectrum peak value; Figure 6 It is the effect of rise time variation on EMI spectrum peak value; Figure 7 It is the effect of fall time variation on EMI spectrum peak value; Figure 8 These are the switching timings of four Si / SiC hybrid devices; where (a) is switching timing A, (b) is switching timing B, (c) is switching timing C, and (d) is switching timing D. Detailed Implementation

[0017] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0018] This invention provides an EMI modeling and spectrum analysis method for Si / SiC hybrid devices, comprising the following steps: S1: Based on the actual switching process of hybrid devices, the common-mode voltage waveform is reasonably simplified to construct an asymmetric trapezoidal wave that can reflect the rising edge, falling edge and conduction stage; It should be further explained that, in actual switching processes, Si / SiC hybrid devices formed by parallel connection of SiC MOSFETs and Si IGBTs, such as... Figure 1 As shown, its switching transient waveform is as follows: Figure 2 As shown. The bus voltage V across the device... DS Simplifications are made as follows: 1) Ignore voltage overshoot during the turn-off process; 2) Assume that V during the turn-on and turn-off processes... DS The rate of change is constant; 3) It is assumed that the voltage rise time and fall time are different. Therefore, it forms Figure 3 The asymmetric trapezoidal wave shown facilitates the analysis of the common-mode voltage V. DS Perform mathematical modeling. Figure 3 In the diagram, V represents the bus voltage across the device. and These represent the rise time and the fall time, respectively. T represents the time from half the rise to half the fall, and T is the period of the asymmetric trapezoidal wave pulse.

[0019] S2: Construct a piecewise mathematical function expression based on the asymmetric trapezoidal wave, and perform a Fourier transform on the piecewise mathematical function expression to obtain the nth harmonic amplitude expression of the common-mode voltage; The piecewise mathematical expression for an asymmetric trapezoidal wave is as follows: (1) According to the Fourier transform formula , for example Perform a Fourier transform to obtain the common-mode voltage V. DS The expression for the nth harmonic S(n) is as follows: As shown.

[0020] (2) (3) in The three integral terms in S(n) are calculated below: 1) First item: (4) 2) Second item: (5) 3) The third item: (6) United The magnitude of S(n) can be obtained from the formula as follows: (7) (8) In the formula, , These are the harmonic frequency and the switching frequency, respectively.

[0021] S3: Take the envelope of the harmonic amplitude according to different frequency bands to obtain the four-segment spectrum peak envelope expression, and determine the corner frequencies between each segment; S(n) represents the nth harmonic, and taking its modulus yields the equation... S(n) represents the amplitude of the nth harmonic component. During EMI testing, it is common to check whether different harmonic components exceed the limits. Therefore, we only need to focus on the amplitude of S(n) when n takes different values. Connecting the amplitudes of S(n) when n takes different values ​​forms the upper envelope of the harmonic components.

[0022] 1) When n is large, the harmonic frequency is... Larger: Take =-1, then |S(n)| reaches its maximum value |S1(n)|: (9) 2) Let When n decreases to At that time, harmonic frequency Decrease: According to the equivalent infinitesimal relation, we have: (10) Pick =j, If the sum is -j, then |S(n)| reaches its maximum value |S2(n)|: (11) 3) As n continues to decrease, and makes At that time, harmonic frequency Further reduction: According to the equivalent infinitesimal relation, we have: (12) Pick Then |S(n)| reaches its maximum value |S3(n)|: (13) 4) When n decreases to 1, |S(n)| reaches its maximum value |S4(n)| as shown in equation (15): (14) (15) The frequency inflection points between |S1(n)| and |S4(n)| are calculated below. Let: (16) Obtain the corner frequency , , As shown below: (17) Therefore, the turning frequencies of each segment of the envelope are shown in equation (17), and the expressions of each segment of the envelope are shown in equation (18).

[0023] (18) From equations (17) and (18), we can see that: 1) When the harmonic frequency is high, the upper envelope of the harmonic components of the asymmetric trapezoidal wave is |S1(n)|.

[0024] 2) When the harmonic frequency is mid-to-high frequency, the upper envelope of the harmonic components of the asymmetric trapezoidal wave is |S2(n)|, and |S2(n)| and |S1(n)| are in A turning point.

[0025] 3) When the harmonic frequency is low to medium, the upper envelope of the harmonic components of the asymmetric trapezoidal wave is |S3(n)|, and |S3(n)| and |S2(n)| are in A turning point.

[0026] 4) When the harmonic frequency is low, the upper envelope of the harmonic components of the asymmetric trapezoidal wave is |S4(n)|, and |S4(n)| and |S3(n)| are in A turning point.

[0027] Taking the logarithm of equation (18), we get equation (19): (19) Equation (19) represents the peak value of the EMI spectrum of the common-mode voltage VDS.

[0028] The EMI spectrum peaks are plotted according to equations (17) and (19) as follows: Figure 4 As shown.

[0029] In the high-frequency range of the spectrum, its slope is -40 dB / dec; in the mid-to-high frequency range of the spectrum, since fc > Therefore Its slope is greater than -20dB / dec and less than -40dB / dec; in the mid-low frequency range of the spectrum, its slope is -20dB / dec; in the low frequency range of the spectrum, its slope is approximately 0.

[0030] S4: Based on the envelope expression, analyze the influence of bus voltage, rise time, fall time and switching sequence on the peak value of the spectrum, so as to guide EMI optimization design.

[0031] The influence of different switching parameters on the peak value of the EMI spectrum is as follows: bus voltage V When the bus voltage VWhen it changes, only its harmonic amplitude is affected, 20lg| S ( n The four segments of )| change at the same amplitude simultaneously, such as Figure 5 As shown, the red line represents the bus voltage. V The voltage is 400V, and the blue line represents the bus voltage. V It is 100V. Specifically, when the voltage increases or decreases, 20lg| S ( n | Move up or down as a whole.

[0032] Ascent Time When the rising time When it changes, its harmonic amplitude and corner frequency change simultaneously, such as Figure 6 As shown, the red line represents the rise time. The rise time is 10ns, and the blue line represents the rise time. It is 30ns. Specifically, when When decreasing, | S 1( n | Increase, meaning the amplitude of the high-frequency harmonic band increases. Changes on 20lg| S 4( n The effect of )| is not obvious; at the same time, when When decreasing, frequency transition Increase, and Changes The impact is not significant. Considering the above two points, Decreasing the frequency will increase the high-frequency components of the harmonics, and vice versa. Increasing the frequency will reduce the high-frequency components of the harmonics.

[0033] Descent time When the descent time When it changes, its harmonic amplitude and corner frequency change simultaneously, such as Figure 7 As shown, the red line represents the descent time. The time is 80ns, and the blue line represents the fall time. It is 40 ns. Specifically, when When decreasing, 20lg| S 1( n )|and 20lg| S 2( n The amplitude of the high-frequency bands and the mid-high-frequency bands of the harmonics increases. Change pair | S 4( n The effect of )| is not obvious; at the same time, when When decreasing, frequency transition Increase, and Changes The impact is not significant. Considering the above two points, Decreasing the frequency will increase the high-frequency and high-frequency components in the harmonic frequency range, and vice versa. Increasing the frequency will reduce the high-frequency and high-frequency components in the harmonic frequency range.

[0034] The impact of switching timing on EMI spectrum peak values ​​is as follows: When different gate switching sequences are used in Si / SiC hybrid devices, the switching order and turn-on / turn-off delays of the hybrid devices will change, thus affecting the rise time. and descent time This invention mainly analyzes, for example... Figure 8 The four switching sequences are shown.

[0035] Because MOSFETs switch faster than IGBTs, the switching timings C and D can be considered similar to the switching timing A, except for the common-mode voltage. V DS rise time and descent time They are different. Although the switching timing B is the opposite of A, its simplification into an asymmetric trapezoidal wave is similar; only the common-mode voltage needs to be considered. V DS of and The following analysis will follow.

[0036] 1) Switching sequence A: The MOSFET turns on first and then turns off. Because the MOSFET switches quickly, the common-mode voltage is... V DS rise time and descent time The smaller the frequency, the more the high-frequency and high-frequency components in the harmonic frequency range will increase.

[0037] 2) Switching sequence B: The IGBT turns on first and then turns off. Because the IGBT's switching speed is relatively slow, the common-mode voltage is... V DS rise time and descent time The larger the frequency, the smaller the high-frequency and high-frequency components in the harmonic frequency range.

[0038] 3) Switching timing C: Simultaneous turn-on, followed by turn-off of the MOSFET. Because the MOSFET switches quickly, the turn-on and turn-off processes can be considered as MOSFET characteristics, with common-mode voltage... V DS rise time and descent time The smaller the frequency, the more the high-frequency and high-frequency components in the harmonic frequency range will increase.

[0039] 4) Switching timing D: Simultaneous turn-on and simultaneous turn-off. Due to the high switching speed of MOSFETs, the turn-on process can be considered as MOSFET characteristics, and the turn-off process can be considered as IGBT characteristics. Common-mode voltage. V DS rise time Smaller, descent time The harmonic frequency components are relatively large, therefore, an increase or decrease in their harmonic frequency components needs to be determined based on... and Detailed analysis.

[0040] In summary, switching sequences A and C have the highest common-mode EMI noise, switching sequence D has moderate common-mode EMI noise, and switching sequence B has the lowest common-mode EMI noise.

[0041] In summary, by adopting the technical solution of this invention, the interference amplitude under different harmonic orders can be quickly predicted without relying on time-domain simulation, which significantly improves the analysis efficiency of EMI characteristics.

[0042] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0043] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for EMI modeling and spectrum analysis of Si / SiC hybrid devices, characterized in that, Includes the following steps: S1: Based on the actual switching process of hybrid devices, the common-mode voltage waveform is reasonably simplified to construct an asymmetric trapezoidal wave that can reflect the rising edge, falling edge and conduction stage; S2: Construct a piecewise mathematical function expression based on the asymmetric trapezoidal wave, and perform a Fourier transform on the piecewise mathematical function expression to obtain the nth harmonic amplitude expression of the common-mode voltage; S3: Take the envelope of the harmonic amplitude according to different frequency bands to obtain the four-segment spectrum peak envelope expression, and determine the corner frequencies between each segment; S4: Based on the envelope expression, analyze the influence of bus voltage, rise time, fall time and switching sequence on the peak value of the spectrum, so as to guide EMI optimization design.

2. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 1, characterized in that, The reasonable simplification in S1 is as follows: ignoring voltage overshoot during the turn-off process, assuming that the rate of change of common-mode voltage is constant during the turn-on and turn-off processes, and assuming that the voltage rise time and fall time are different.

3. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 1 or 2, characterized in that, The piecewise mathematical function expression for the asymmetric trapezoidal wave is: ； In the formula, This refers to the bus voltage across the device. and These represent the rise time and the fall time, respectively. The time taken from half the rise to half the fall. The period of the asymmetric trapezoidal wave pulse.

4. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 1, characterized in that, The amplitude of the nth harmonic The expression is: ； in: ； ； ； In the formula, , These are the harmonic frequency and the switching frequency, respectively.

5. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 1, characterized in that, The expression for the four-segment spectral peak envelope in S3 is as follows: High frequency band: ； Mid-to-high frequency band: ； Mid-to-low frequency band: ； Low frequency band: ； The transition frequency is: 。 6. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 1, characterized in that, The switching timing in S4 includes four modes: Switching timing A: MOSFET is turned on first and then turned off; Switching sequence B: IGBT is turned on first and then turned off; Switching timing C: All switches are turned on simultaneously, and the MOSFETs are turned off later. Switching sequence D: Simultaneous on and simultaneous off; By analyzing different time series and The changes in these parameters are used to predict the trend of EMI spectrum peak values.

7. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 6, characterized in that, Switching timing sequence A and switching timing sequence C, rise time and descent time The harmonic frequency is smaller, and the high-frequency components in the middle and high-frequency bands increase; Rise time in switch sequence B and descent time The harmonic frequency is relatively large, and the high-frequency components in the middle and high-frequency bands are reduced; The increase or decrease of the D harmonic frequency component in the switching timing needs to be based on and Detailed analysis.

8. The EMI modeling and spectrum analysis method for Si / SiC hybrid devices as described in claim 1, characterized in that, The voltage of the S4 bus only affects the harmonic amplitude and does not change the corner frequency; reduce or This will increase the amplitude of the high-frequency or mid-high-frequency harmonics and increase the corresponding turnaround frequency.

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