3-D Electromagnetic Modeling and Analysis of Electromagnetic Field Couplings of EMI Filter Capacitors

This paper presents a calculation of self-inductance and mutual couplings between EMI capacitors based on analytical equations and 3D simulation (Finite Element Method (FEM) and Method of Moments (MoM)). The analytical results are validated using numerical results. As an internal structure of a real capacitor is quite complex, in 3D simulation, a model of a capacitor is based on the same external geometrical properties. The self-inductance and the mutual couplings are calculated as a function of external geometrical properties, their orientations, and distances between them. The influence of parasitics such as magnetic couplings, PCB trace inductances between DM capacitors, and ground trace inductances of CM capacitors on the DM and CM attenuation are analyzed using numerical and experimental methods. Besides, the impact of the PCB layout on the magnetic coupling is analyzed. The parasitic reduction (Opposite Current Direction - OCD) technique between two DM capacitors is investigated considering parasitics of PCB traces and magnetic couplings among them as well as their possibilities are identified. The numerical results are verified by the measurement results.