Three‐phase bidirectional isolated LLC resonant DC‐DC converter for DC microgrid applications

Abstract

SummaryDC microgrids rely strongly on bidirectional dc‐dc converters responsible for managing the power flow among distinct loads and renewable energy sources like fuel cells and batteries. In this context, this work presents a three‐phase inductor‐inductor‐capacitor (LLC) resonant dc‐dc converter with high‐frequency isolation and bidirectional power flow capability, employing phase‐shift control and frequency modulation. The resonant tank takes advantage of using the leakage inductance and the magnetizing inductance of the high‐frequency transformer (HFT), which allows for improving power density. The active switches operate with a fixed duty ratio of 50% so that the converter can always achieve zero‐voltage switching (ZVS). The mathematical analysis is carried out based on a single‐phase representation of the converter, which considers only the fundamental components. A dynamic model is derived using the gyrator theory, which allows representing the converter as a frequency‐controlled current source to regulate the output voltage. In addition, the power flow direction is determined from the estimation of an ideal phase‐shift angle for each frequency aiming to control the output power. An experimental prototype is implemented and thoroughly assessed to demonstrate that the introduced topology is feasible for dc microgrids and other applications that require bidirectional power flow.