EMI Filter Integration for GaN Power Module Using Air-Cured Magnetic Composite

Severe electromagnetic interference (EMI) issues in wide-bandgap (WBG) power electronics systems result in larger filter sizes to attenuate noise, which compromises the high power density brought by WBG devices. To mitigate the high-frequency EMI noises of WBG systems, integrating a common-mode filter inside the power module is an effective way of managing parasitics in the noise propagation paths and thereby improving the filter performance. However, the magnetic core of a common-mode choke (CMC) takes up considerable height and weight, which lowers the power density of a module. In this paper, an air-cured and module-compatible manufacturing methodology is developed using permalloy-epoxy magnetic composites for the integrated CMC inside a GaN power module.The magnetic composite is mixed into a paste texture and can conveniently mold the power module to form the CMC, improving the space utilization and power density of the whole module. This also offers a potential magnetic integration solution for other WBG power modules or circuits. One of the composites has a real part of the complex permeability of 13.5 under high frequency with low core-loss density. A 3-D finite-element model is built to predict the inductance of the over-molded CMC cured with the designed magnetic composite. The manufacturing process of the over-molded CMC is explained and the impact of the magnetic material on the power module parasitics is analyzed. The benefits of the over-molded CMC in EMI reduction and power density improvement are verified by test results, and some suggestions for future optimization are provided.