Shielding Effect of High Frequency Coaxial Transformers Used in Bi-Directional DC-DC Converter for Energy Storage Systems

Abstract

Existing DC-DC converters used in the energy storage systems are usually bulky and inefficient. This is because existing transformers used in the DC-DC converter operates in a low frequency of 60 Hz. While operating in low frequency, it requires larger magnetic core of the transformer and larger passive components to be used in the switching circuit. Therefore, the volume of converters can be greatly reduced by increasing the operating frequency. For this reason, this paper introduces an isolated high frequency (HF) coaxial transformers which operates from 100 kHz to 300 kHz with >99% power efficiency. The HF coaxial transformer is suited for the use in the converter of energy storage systems such as those in electric vehicles and renewable energy systems because of its small size, compact structure, broad power range as well as high energy efficiency. Having said that, the electromagnetic interference (EMI) issue arises while the operating frequency increases due to the high frequency noise. Hence, a Faraday shield was inserted to manage the increased coupling capacitance of transformers resulting from the higher operating frequency. The shielding effect of the HF coaxial transformer was analyzed and discussed in this paper.