Experimental Verification of Two-Stage Power Converter with Current-Fed Soft-Switching Front-End for Battery Storage Applications

This paper presents a two-stage power system that consists of a novel bidirectional current-fed DC-DC converter module for interfacing with lithium iron phosphate battery, followed by a single-buck inverter for grid interface. Additional benefit of the proposed two-stage converter lies in the intermediate DC-link between two stages that allows connection of other energy sources, such as PV. The proposed converter offers galvanic isolation, high voltage step-up factor and power factor correction. The operation principle and control system structure of the case study converter are described. Due to the accommodation of a special phase-shift modulation algorithm, the proposed front-end converter features natural voltage clamping and soft-switching of all semiconductor devices without additional components such as snubbers and clamping circuits. Parameters of the converter were estimated in accordance with residential battery energy storage system requirements. A 500W prototype converter was developed to validate theoretically estimated characteristics of the converter, including the soft-switching range, transfer function and design constraints. Experimental waveforms as well as efficiency for both charge and discharge operation modes are presented and analysed.