ANALYSIS AND DESIGN OF SOFT-SWITCHING CURRENT-FED TOPOLOGIES WITH NEW MODULATION TECHNIQUES FOR DC MICROGRID AND ENERGY STORAGE APPLICATIONS

Abstract

The demand for versatile energy storage system is increasing in More Electric Vehicles (MEVs) and renewable energy system, requiring power electronic systems for interfacing. However, design of such power converters is challenging because they must be rated for peak power, but medium to light load efficiency is critical. Also, wide variation of energy storage voltage, large voltage boost requirement and bidirectional operation makes it difficult to achieve good performance over a wide operating range. The Current-Fed Dual Active Bridge (CFDAB) converters with DC inductor in the Low Voltage (LV) side are a suitable choice but suffer from voltage spikes across the turning off LV devices. This is due to the non-zero parasitic inductances at the switching node. In this research work, modulation scheme to avoid the voltage spike while simultaneously improving operating range efficiency is developed. For bidirectional operation, the reverse direction performance is addressed separately and the converter is optimized for the entire operating space. The research work focusses on software-only solutions which are simple, easy to implement and yet significant improvement in the performance is observed.