Hetero-Magnetic Swinging Inductor (HMSI) and Its Application for Power Factor Correction Converters

A variable inductor concept based on a magnetic structure consisting of a composite of magnetic materials is introduced to meet designed inductance function of current. A design of the inductor, termed hetero-magnetic swinging inductor (HMSI), was fabricated using a toroid core with a gap that was filled by a custom-developed low-permeability magnetic powder + polymer material. Having the gap filled with the magnetic material allowed for greater flexibility in L-I design with added benefit of low fringe field. We applied this swinging inductor to a Critical Conduction Mode (CRM) Boost power factor correction (PFC) converter to reduce its switching frequency variation range. First, the required L-I curve of the HMSI needed for narrow range of switching frequency was calculated. Then, the HMSI core structure consisting of two magnetic materials was designed. Circuit simulations showed that for a 110-Vrms input, the converter with the HMSI had a switching frequency variation factor, defined as Δf/fmin, six times less than that of the converter using a linear inductor. A prototype of the HMSI was fabricated and tested. The effectiveness of using the HMSI to narrow the range of switching frequency variation was verified in a 150 W CRM PFC converter.