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The hybrid common-mode (CM) electromagnetic interference (EMI) filter (HEF) consists of active EMI filter (AEF) and passive EMI filter (PEF). The PEF has higher attenuation at high-frequency band and the AEF is better at suppressing CM EMI at lower band, so they are complementary to each other. However, traditional HEF is designed to satisfy the largest required attenuation and it ignores that CM EMI has multiple resonance peaks in frequency domain, so it leaves unnecessary margins in some frequency bands and leads to an undesired overdesign. To address the shortcoming, this article investigates the attenuation adjustability and puts forward a novel design method for the HEF. First, traditional HEF design is introduced, whose limitation is that unnecessary margins and undesired overdesign are caused. Then, the attenuation adjustability is analyzed and it allows the attenuation to change flexibly due to AEF's high degree of freedom. On this basis, the HEF design method is proposed. It can fit the required attenuation instead of only aiming at the largest attenuation, and the undesired overdesign can be avoided. The method is verified experimentally in a SiC-based H-bridge inverter, which shows that the inductance of the CM choke is reduced by 73%.
Chen et al. (Mon,) studied this question.