Influence of parasitic effects on passive cancellation of common mode noise in a boost converter

Passive cancellation of common mode (cm) noise is a very promising alternative to a conventional cm filter. The basic idea has already been described in literature. However, to the authors´ knowledge, a thorough investigation of parasitic effects has not been published yet. It turns out that the parasitic effects are crucial for this passive cancellation method. Therefore it is of great interest to investigate this influence. In combination with a finite differential mode (dm) filter capacitor C_dm a second capacitor C_gnd is required to reach theoretically an infinite attenuation due to a perfect compensation. However, in practice this is prevented by the transformer´s leakage inductance. An analysis based on frequency-response plots and phasor diagrams allows quantifying the influences. Minimizing the leakage inductance by an optimized transformer design results in the best attenuation of cm noise. Finally, the theoretical results are verified in a test set-up.