计及混合噪声的集成式EMI滤波器设计

Integrated EMI Filter Design Considering Mix-Mode Noise

噪声测量是EMI滤波器设计的基础,噪声测量中由于噪声电流的不平衡,一种形成机理类似于共模(CM)噪声却通过差模(DM)模块进行抑制的噪声被称为"混合(MM)噪声",该噪声对滤波器的设计具有重要的影响。通过分析MM噪声的产生机理,将其区别与传统的DM噪声与CM噪声;探索了DM模块在MM噪声抑制中的作用,DM模块的功能由利用阻抗不匹配原理对噪声进行抑制变为利用阻抗不匹配以及阻抗平衡分别对传统DM噪声和MM噪声进行抑制。以集成式EMI滤波器中的平面型EMI滤波器和母线型EMI滤波器为例,研究了MM噪声对该类滤波器设计的影响,并阐述了考虑MM噪声后对集成式EMI滤波器的制作、材料等方面的影响;基于传统噪声理论及MM噪声理论分别设计了一台EMI滤波器。研究表明,计及MM噪声后设计的EMI滤波器性能更优良。

Noise measurement plays an important role in the design of EMI filter. Due to the imbalance behavior of noise current flowing through a LISN, the mix-mode（MM） noise is generated. The generation mechanism of the MM noise is similar to the common mode（CM） noise, but it is suppressed by using differential mode（DM） capacitor. Based on the study of MM noise, the differences between the MM noise and the conventional noise（including conventional DM noise and CM noise） are explored. The suppression mechanism of MM noise is explored. The function of DM part is attributed into two distinct parts： impedance mismatch for conventional DM noise and noise current balancing for MM noise. The bus-bar EMI filter and the planar EMI filter, representative EMI filters of integrated EMI filters, are analyzed. Based on the analyses, the effects of MM noise emission on the design of bus-bar EMI filter and planar EMI filter are explored. The effects on the selection of material and the production of integrated EMI filter are elaborated. The newly designed examples considering MM noise are presented and experiments are carried out to verify the analysis. The effectiveness of the newly designed EMI filters on the suppressing of noise and the accuracy design of the parameter of EMI filters are shown from the conducted experiments.