Optimization　of　winding　resistance　for　litz　wire　inductors　is　essential　to　reduce　losses　and　improve　energy　transfer　efficiency　in　electrical　power　systems.　In　this　study,　an　approximate　model　for　the　optimization　of　winding　resistance　in　litz　wire　inductors　based　on　Dowell＇s　equation　is　developed　in　three　frequency　ranges.　The　proximity　and　skin　effects　are　analysed　separately　and　subsequently　combined　to　obtain　an　approximation　with　minimum　theoretical　error.　Two　error　functions　are　defined　to　determine　the　frequency　ranges　for　which　the　approximation　is　valid.　Based　on　this　Dowell＇s　model　approximation,　it　is　found　that,　with　the　other　parameters　of　the　inductors　fixed,　both　the　porosity　factor　and　conductivity　have　an　optimal　value　that　minimizes　AC　resistance　for　the　litz　wire　windings.　Thus,　expressions　for　the　optimum　porosity　factor　and　conductivity　are　derived,　the　optimization　schemes　under　different　practical　engineering　conditions　are　also　given.　The　theoretical　results　are　in　good　agreement　with　the　experimental　measurements,　which　indicates　that　the　proposed　model　is　valid　for　three　frequency　ranges,　and　the　proposed　optimization　method　is　practical　and　suitable.