CCM boost inductor design

Piotr Wyderski · 2019-07-28T14:00:36+00:00

Hi, I would like to make a low-loss boost PFC converter for the following parameters: 150kHz switching frequency, 180-250VAC input, 600V output at 500W. It should operate in CCM with 20% deltaIL, so the inductor will be pretty large: 1.2mH at 4.6A_peak. Basically, I am considering two options of winding it: a gapped low-loss ferrite core (3C95 or similar material) or an alloy powder E core EMS-0432115-060. The latter is currently my preferred choice due to its great wide-swing saturation characteristics (~1.8uH@0A and still a nice value of 600uH at a 10A surge). Unfortunately, it will require 108 turns, so for a bobbin 27mm wide and relatively thin 1mm diameter wire means 4 layers of windings. I am afraid this can introduce some nasty resonances and make the AC resistance worse due to the proximity effect. OTOH, this is a 20% CCM inductor, so the AC component is only about 800mA in the worst case. So, should I consider winding it with litz wire (7x0.4mm is probably the thickest braid I can fit there) or ignore the AC component entirely and go to the lowest DCR achievable, i.e. a 1.2mm solid wire? I don't think I can obtain a square 1x1mm magnet wire, the closest purchasable size is 2x1mm, which for sure will not fit. The alternative is a planar E58 core wound with 4 layers of 2.5mmx1mm rectangular wire (54 turns in total). But the inductor would be about 2x the size of the powder core one and have a dangerously sharp saturation curve. The boost will be based on a SiC device, but I don't want to go into the MHz switching range in order to have a physically smaller inductor -- the parameter I optimize is raw efficiency, not power density. So I see no point in transforming winding losses into switching and core losses. Any thoughts, please? Best regards, Piotr