Design and Potential of EMI CM Chokes with Integrated DM Inductance

A common-mode (CM) choke is one of the major filtering components used in electromagnetic interference (EMI) filters that impede the flow of common-mode current in the system. Besides, a common-mode choke also offers a finite differential-mode (DM) inductance in the form of leakage inductance. In general, the leakage inductance is small, which necessitates extra DM inductors and leads to a large filter size. In this paper, a single-phase CM choke is designed with an integrated DM inductance for use in EMI filters, based on a flux bypass inside the toroidal core. The DM inductance of these chokes can be altered by redesigning the windings, while the CM inductance remains identical to a conventional CM choke. The design and effectiveness of them are further supported by theoretical, simulated, and measurement results and core saturation analysis. Finally, an extension to three-phase CM chokes with integrated three-phase DM inductance is discussed.