Compact Spiral Transformer Design for High-Efficiency Interleaved Flyback Converters in Solar Power Systems

Abstract

This paper explores the design, modeling, and optimization of a spiral transformer integrated into an interleaved flyback converter tailored for photovoltaic (PV) applications. The transformer features two square planar spiral coils with an outer diameter of 9000 µm and an inner diameter of 6000 µm, yielding primary and secondary inductances of 0.128 µH and 0.226 µH, respectively, at a 5 MHz operating frequency. The miniaturized design includes 3 primary turns and 4 secondary turns, with conductor widths of 500 µm and 300 µm, respectively. An electrical model accounts for parasitic effects, such as series resistances (0.195 Ω for primary, 0.282 Ω for secondary) and capacitances (inter-turn and oxide layer), which are minimized to boost efficiency. Frequency-dependent behavior is analyzed using MATLAB, identifying a resonance frequency of 20 MHz and a coupling coefficient of 0.87. The interleaved flyback converter, simulated in PSIM, delivers a stable 48 V output voltage and 3.2 A output current from a 162 W input, achieving 95% efficiency. This work validates the potential of compact, high-efficiency transformers for advancing PV energy conversion systems.