A high frequency model of toroidal chokes for EMC filtering

Chokes are crucial in power electronics applications to block the propagation of high-frequency disturbances produced in switching events. At high frequencies, the real behavior of a choke can differ significantly from its nominal behavior due to the frequency-dependency of core materials and due to parasitic couplings introduced by the windings. This paper presents an accurate, versatile, and computationally efficient method to compute the parasitic couplings and predict the frequency-dependent impedance of the choke. Comparison with measurements of sample chokes with ferrite and nanocrystalline cores show excellent agreement in the entire EMC frequency range of 150 kHz to 30 MHz. Multiple self-resonances of the choke can be correctly described.