Vector Based Transformer Winding Power Loss Calculation and Reduction for Arbitrary Currents

This paper proposes a technical approach to calculate the AC power loss of transformer windings for the currents with arbitrary shapes and phase-shifts. AC winding power loss formulas are derived based on vector form, and they are important for analyzing the power loss due to skin and proximity effects. Based on the proposed approach, guidelines to optimize transformer winding structures were proposed and applied to a transformer in an active-clamp Flyback power converter. The auxiliary, CM EMI cancellation, and shielding windings commonly used in power products are all taken into consideration in the guidelines. Simulations and experiments were conducted to verify the developed theory and techniques.