Efficiency enhancement of the high-frequency isolated grid-connected converter for the battery energy storage system

High-frequency (HF) isolated grid-connected converters for a battery energy storage system have been extensively researched in recent years. However, due to the HF isolated energy conversion link, the operation efficiency is relatively lower than that required in mass adoption. The topology of the HF isolated grid-connected converter proposed in this paper features a dual active bridge (DAB) converter containing a multi-winding HF transformer and two multi-arm converters. Through modifying the operation modes of the DAB converter, the commutation inductor in the soft switching process can be adjusted according to the load conditions. Thus, the operation efficiency of the grid-connected converter is improved under heavy load and at light load. Meanwhile, the modifying points of the operation modes are selected based on the power dissipation models. Additionally, the control system for the proposed DAB converter is designed based on the small signal model, and the parameters of the regulator are also calculated. Finally, the theoretical analyses are validated by the experimental results on a prototype circuit.