An Isolated DC-DC Converter With Multiple Cascaded Choppers Featuring RMS Current Reduction Toward Resilient Power Grids

The penetration of renewable energy resources (RES) is decreasing the inertia of current power grid due to their intermittent nature. Thus, the introduction of energy storage systems (ESS) can cancel this influence out, thereby increasing the power grid resilience. This article proposes a novel isolated dc-dc converter designed for ESS in low voltage dc (LVDC) power grids. This converter aims to facilitate the development, installation, and efficient operation of ESS. The proposed converter is based on the conventional three-phase dual-active-bridge (TP-DAB) converter and incorporates a three-phase Yn-Y transformer with a three-limb core, as well as auxiliary converters using multiple cascaded bidirectional choppers connected to the primary side of the transformer. Unlike the traditional TP-DAB converter, which suffers from large converter currents due to reactive current, the proposed converter features the fundamental-frequency unity-power-factor operation, effectively reducing the root-mean-square (RMS) and peak currents under a wide range of operating conditions, leading to higher efficiency compared with the TP-DAB converter. The article presents the operating principles and control methods of the proposed converter and compares its performance with the conventional TP-DAB converter in terms of RMS and peak currents and power losses. The feasibility and practical applicability of the proposed converter are verified through a 150 V, 2.5 kW downscaled prototype.