Shielding effect of high frequency power transformers for DC/DC converters used in solar PV systems

Conventional high frequency power transformers are configured without protection to avoid parasitic effects. Therefore this paper presents and investigates a FEM technique and measurement results for planar and coaxial high frequency power transformers used for DC/DC converters in photo voltaic (PV) power systems. The winding structure includes a Faraday shield between the primary and secondary windings and is designed to minimize skin and proximity effects, eddy current losses, the leakage inductance, and the inter winding coupling capacitance. Finite Element Method is employed to analyze the magnetic flux and eddy current distributions, and to accurately calculate the intra- and inter- winding capacitances based on the theory of capacitances in a multi-conductor electro-magnetic system. The two different kinds of HF transformers have been tested and experimentally simulated. The measured results demonstrate, in contrast to non shielded transformers, that the shielded transformers have achieved the expected results with a relatively small coupling capacitance, compared with the conventional high frequency transformer. This shield decreases the inter-winding coupling capacitance Cps and the leakage induction.