Average Modeling of High Frequency AC Link Three-Port DC/DC/DC Converters

Abstract

The current transition towards renewable energies has led to an increased utilization of Photovoltaic (PV) sources and battery energy storage systems to complement the PV panels. To facilitate energy transfer among PVs, batteries, and loads, multiple converters are required. Thus, this transformation in the energy system has resulted in an increase in converter-interfaced elements. Within this context, three-port converters allow for replacing multiple converters with a single one. These three-port converters use a high-frequency AC resonant link for the bidirectional transfer of energy across the different ports. This architecture uses multiple switches and has a variable operating frequency. These characteristics make the simulation of these converters computationally heavy. Thus, averaged models are required, especially for simulating multiple converters connected in parallel or composing a microgrid. In this paper, an averaged model for this type of converter is developed. The methodology is first demonstrated and applied to a two-port DC/DC converter, and subsequently extended to the three-port DC/DC/DC version. Afterwards, control strategies for three-port DC/DC/DC converters are proposed based on the elements connected to their ports. The developed model for three-port DC/DC/DC converters is then implemented in an islanded DC microgrid to demonstrate their parallel operation. The proposed developed averaged models and the test DC microgrid are implemented in MATLAB/Simulink.