Optimizing AC and DC winding losses in ultra-compact, high-frequency, high-power transformers

Removing heat from the windings of a high power (>100kW) transformer is a significant thermal challenge, especially in the case of the ultra-compact electric vehicle inductive charging transformer. In this paper, nine different transformer design techniques are: outlined, analyzed and compared for optimization of the primary and secondary winding resistances to minimize copper lasses in a high-power, high-frequency transformer, For the inductive charging transformer example illustrated, these techniques reduce the total winding losses by as much as 5 to 1 and the AC winding losses by 14 to 1. The techniques used are a mixture of well-known approaches, such as winding interleaving, and other lesser-known approaches, such as flux shaping. The winding losses are calculated using a two-dimensional Finite Element Analysis (FEA) program, and using one-dimensional equations for comparative purposes. These techniques result in a high-power transformer with a power density greater than 1300 W/in(3).