CST電源濾波電路模擬（三）——柳暗花明又一村

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CST濾波模擬系列在2022年已經分享了兩期，分別是：
CST電源濾波電路模擬（一）——紙上得來終覺淺
CST電源濾波電路模擬（二）——於無聲處聽驚雷
本期重點在於電源傳導問題中的磁性元件近場耦合問題的模擬。

遙想筆者當年，CE問題撲朔迷離，山重水複，偶然發現近場耦合問題，瞬間峰迴路轉，柳暗花明。隨著電源模組日益向高頻，大功率，小型化的趨勢演進，近場耦合引發的CE問題早已屢見不鮮。下圖清楚地展示了兩個磁性元件之間的近場耦合效應。

The image consists of two simulation plots. The left plot shows a vector field with arrows indicating the direction and magnitude of a magnetic field around a circular and a rectangular object. The right plot displays a color map of the magnetic field intensity around the same objects, with a color scale ranging from blue (low intensity) to red (high intensity). Both plots include a color bar indicating the magnetic field strength in A/m, and coordinate axes are shown in the bottom right corners.

模擬模型

本期研究的模擬模型為共模濾波電路與BUCK電源電路的組合，具體模擬模型細節如下圖所示：

【電路模型】
電路模型包括供電電源(SOURCE)、LISN、EMI濾波電路、BUCK電源電路。

The image depicts an electrical circuit diagram with various components labeled. The circuit includes sections for SOURCE, LISN, EMI filter, SWITCHING LOOP, and LOAD. Key components include capacitors, resistors, inductors, diodes, and a transformer. The diagram shows the flow of current through these components, illustrating how the circuit is designed to function.

【3D模型】
為驗證兩個磁性元件之間的低頻近場耦合效應，在3D模型中增加金屬隔板，如下圖所示，模型A的濾波電路和BUCK電源電路在同一個腔體內，模型B二者則分佈在兩個腔體內。

The image shows two models labeled as Model A and Model B. Both models contain a circular coil structure and various electronic components. Model A has a single compartment with a filter circuit and a BUCK power circuit. Model B has a metal isolation plate dividing the filter circuit and the BUCK power circuit into separate compartments. The text in the image is in Chinese, with labels indicating the different circuits and components.

【場路聯合模擬模型】如下圖所示，其中PCB、金屬外殼、共模電感、BUCK功率電感均採用3D模型，其他電路元件採用電路模型。

This image shows a detailed circuit diagram with various components and connections. The diagram includes a source, LISN (Line Impedance Stabilization Network), EM filters, a switching loop, and a load. The central part of the diagram features a PCB (Printed Circuit Board) with multiple connections leading to different parts of the circuit. The components are connected through lines representing electrical connections, and there are several capacitors, resistors, and inductors depicted. The diagram is labeled with terms such as 'SOURCE,' 'LISN,' 'EM filter,' 'SWITCHING LOOP,' and 'LOAD,' indicating the different sections and their functions within the circuit.

模擬結果

【模擬結果分析–時域模擬波形】

此BUCK電源的輸入為12V，工作頻率為488kHz，佔空比為48.7%，輸出電壓約5V。下圖分別為開關訊號電壓波形，BUCK電源輸出電壓波形及電流波形。

The image shows a graph titled 'TD Voltages' with the x-axis labeled 'Time / us' and the y-axis labeled 'Voltage / V'. The graph displays a green waveform labeled 'Port1' that oscillates between approximately 0 V and 1.5 V in a periodic manner. The waveform has a square shape, indicating a switching signal voltage waveform. The time range on the x-axis is from 0 to 10 microseconds, and the voltage range on the y-axis is from -1 V to 2 V. The title in Chinese at the top left corner reads '开关信号电压波形', which translates to 'Switching Signal Voltage Waveform'.
A graph titled 'BUCK电源输出电压波形' shows the output voltage waveform of a buck converter over time. The x-axis represents time in microseconds (us) ranging from 0 to 1000, and the y-axis represents voltage in volts (V) ranging from 0 to 5.5. The red line indicates the voltage, which initially spikes to about 5.3V at around 50us, then gradually stabilizes to approximately 4.5V.
A graph titled 'BUCK電源輸出電流波形' shows the output current waveform of a BUCK power supply. The x-axis represents time in microseconds (us) ranging from 0 to 1000, and the y-axis represents current in amperes (A) ranging from -1 to 10. The waveform starts at 0 A, peaks at around 8.5 A at approximately 50 us, and then stabilizes around 1.5 A for the remainder of the time.

【模擬結果分析–傳導雜訊】

從傳導雜訊模擬結果的頻譜比較可知，採取金屬分腔後，開關頻點的基頻及其高次諧波均有明顯的降低

A graph showing FD Voltages [Magnitude] with Voltage (dBuV) on the y-axis and Frequency (MHz) on the x-axis. The graph compares two models, 模型A (red) and 模型B (blue), labeled as 'Lisn Diff' and 'Lisn Diff_isolated' respectively. The red and blue lines show voltage variations across frequencies from 0.15 MHz to 30 MHz, with notable peaks at certain frequencies, indicating differences in voltage behavior between the two models.

紅色曲線為模型A的模擬結果，藍色曲線為模型B的模擬結果。

【模擬結果分析–表面電流】

在3D場模擬介面中，分別加入表面電流監視器（surface current monitor），頻點分別為開關頻點0.4878MHz，以及10MHz和20MHz左右。從下圖0.4878MHz的表面電流模擬結果比較可知：

  1. 0.4878MHz的噪音源為BUCK功率電感；
  2. 0.4878MHz受到BUCK功率電感與濾波電路共模電感之間的耦合影響較大。
A simulation image showing the surface current distribution at 0.4878 MHz on a circuit board. The image highlights two components: a common mode choke in the filter circuit and a BUCK power inductor. The surface current is represented by a color scale ranging from blue (low current) to red (high current). The maximum surface current is 4508.13 A/m. The text in the image is in Chinese, with labels pointing to the components and a description of the model and frequency.
A simulation image showing the surface current distribution at 0.4878 MHz on a circuit board. The image highlights two components: a common mode choke in the filter circuit and a BUCK power inductor. The surface current is represented by a color scale ranging from blue (low current) to red (high current). The maximum surface current is 6934.07 A/m. The text in the image is in Chinese, with labels pointing to the components and a description of the model and frequency.

從下圖10.732MHz的表面電流模擬結果比較可知：

  1. 10.732MHz的雜訊源為BUCK電源PCB上的功率開關迴路；
  2. 10.732MHz的噪音路徑為PCB功率開關的迴路的空間近場輻射及傳導。
The image shows the surface current distribution at 10.732 MHz on a circuit board. It highlights a PCB layout with annotations 'Model A - No Metallic Partition 10.732 MHz Surface Current' and 'PCB Power Frequency Switching Circuit.' The color bar indicates the range of current densities, from 0 to 1.5 A/m. The bottom left text shows the maximum surface current as 14.5622 A/m.
This image shows the surface current distribution for Model B at 10.732 MHz. The highlighted areas indicate the positions of the metallic partition and the PCB power frequency switching circuit. The color bar shows the range of current densities from blue (low) to red (high).

同樣從20.951MHz表面電流模擬結果可知，20.951MHz的雜訊源也是BUCK電源PCB上的功率開關迴路。

The image shows the surface current distribution of Model A at 20.951 MHz without a metallic partition. The highlighted areas indicate the positions of the PCB power switching circuit. The color bar on the right shows the current density range from 0 to 0.001 A/m. The color map displays various regions with different current densities.
The image shows the surface current distribution of Model B at 20.951 MHz with a metallic partition. The highlighted areas indicate the positions of the PCB power switching circuit. The color bar on the right shows the current density range from blue (low) to red (high). The color map displays various regions with different current densities.

綜上所述，開關頻點488kHz的雜訊振幅受BUCK功率電感的太空近場輻射影響較大，而10MHz以上的高頻段雜訊源頭為功率開關迴路。因此透過合理的佈局佈線，減少功率電感與濾波電感之間的耦合，減少開關環路面積，能夠有效抑制開關電源傳導雜訊。

The image shows a graph comparing the FD Voltages (Magnitude) in dBuV against Frequency in MHz. The graph has two sets of data: 'Lisn Diff' in red and 'Lisn Diff_isolated' in blue. The x-axis represents frequency ranging from 0.15 MHz to 30 MHz, and the y-axis represents voltage ranging from -60 dBuV to 120 dBuV. The graph highlights two main sources: 'BUCK功率电感' and 'PCB功率开关电路', both with the path '空间近场辐射及传导'. The red data shows higher peaks compared to the blue data, indicating differences in voltage magnitudes between the two conditions. The graph is annotated with circles emphasizing significant peaks around 0.5 MHz and 10 MHz.

模擬總結

【CST電源濾波電路模擬總結】

  1.  CST場路聯合模擬，可進行完整的電源電路的傳導雜訊模擬。並透過三維電磁場全波模擬，綜合考慮電源上高功率磁性元件的近場耦合效應，PCB功率開關的環路輻射及耦合效應，PCB寄生參數的影響以及金屬結構對電磁場的影響等因素。
  2. 在進行場路聯合模擬建模之前，簡單的電路模擬是非常必要的。電路模擬能夠幫助我們快速分析傳導雜訊的源頭和路徑，進而建立正確的3D模型。
  3. 磁性元件作為電源模擬的關鍵部件需要單獨建模，並對其基本特性如感量，阻抗等進行模擬。為提高效率，可以使用CST 的低頻工作室中的MS solver/LF solver。
  4. CST模擬結果中電場/磁場/表面電流等2D/3D結果，可以直觀地表現出傳導噪聲的源頭及路徑，從而可以有的放矢的給出CE整改方案。
  5. 電源電路傳導發射模擬是系統級的模擬，看似簡單，其實很難。建議從部件級模擬開始，由簡及難，定性不定量。

原文轉載來自: Wang Jieyu – CST电源滤波电路仿真（三）——柳暗花明又一村

系列文章：

CST電源濾波電路模擬（一）——紙上得來終覺淺
CST電源濾波電路模擬（二）——於無聲處聽驚雷

看更多其他文章：

CST電動車EMC模擬（九）——實現車輛整體模型的自動化簡化
CATIA：改變設計和工程格局的數位建築師
Modelithics：使用集總元件濾波器推動更高的頻率

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