Hey guys, I am currently designing an inductor for a boost converter. It is to be run at 10A DC with small ripple, about 0.4A peak-to-peak. Switching frequency is at 100kHz and the chosen core is a High Flux toroid core. I have Litz wire (small cross-sectional area wires bundled together) in which the diameter of the strands that bundle up are equal to the skin depth at 100kHz. Well, the DC resistance of the wire is 20milliohms which is good but I have a problem with the AC resistance.
I am measuring my AC resistance with the use of the LCR meter using the ESR parameter along with the Ls parameter (measuring inductance with the ESR). When I have not wound my wire, in other words it's just the plain wire, the ESR is at 20 milli ohms at 100kHz but then when I have wound it to the core, the ESR measured is at 3 ohms! So, with a 0.4A peak-to-peak ripple, there will be a 1.2V AC voltage ripple added to the inductor just due to this skin effect and this might cause problems for me. I am concerned with what I can do, and if whether or not what I am measuring is accurate? I have repeated it a number of times and it seems to be the case. I thought that wire skin effect is solved by using Litz wire, the diamater chosen to match the skin depth and it did turned out good when the wire is not wound to the inductor. But when the wire was wound, it's 3 ohms so is this due to the core? Can you explain the phenomenon?
If this is not a wrong interpretation and this is really due to the core can you suggest some tips for me? I have lots of turns because I am preventing my inductor to saturate at the volt-seconds it will be experiencing and I already chose the number of turns such that when I input a pulse-wave to the inductor using a signal generator, the pulse-wave does not get distorted so I cannot reduce the number of turns. Also, the thickness of the wire itself is already chosen for the 10A. The winding has already occupied all space of my inductor, well it's a single layer winding so increasing parallel strands to reduce resistance isn't really gonna' work unless I wound the inductor in double layer.