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

Removing heat from the windings of a high power (>100 kW) 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 losses 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/sup 3/.