Structural design of a common-mode inductor with metallic casing for improved high-frequency performance

The high-frequency common-mode (CM) attenuation of EMI filters for power converters in electric vehicles is often degraded by the equivalent parallel capacitance between the windings of the CM choke, which limits further miniaturization of the systems. This work presents a simple method to improve CM attenuation by exploiting a metallic casing combined with an injected dielectric material to generate a compensating capacitance around the CM choke. A distributed-parameter model was developed to determine the optimal casing configuration, and the proposed concept was validated through circuit simulations and experimental measurements. The results confirmed that the method effectively enhanced CM attenuation above 1 MHz. Because the metallic casing can utilize the existing converter housing, the proposed approach requires no additional components or cost and provides a practical, compact solution for power converter design.