Analysis of a DC/DC converter for centralized energy storage in HVDC applications

Abstract

This work introduces a modular converter designed to integrate a high-capacity Energy Storage Systems (ESSs) based on supercapacitors into a High Voltage Direct Current (HVDC) link. Unlike conventional approaches that distribute stored energy among multiple series-connected sub-modules, this methodology enables the storage of a substantial amount of energy in a single ESS unit, reducing complexity. The proposed converter topology consists of two branches of half-bridge and full-bridge sub-modules, ensuring operational flexibility and bidirectional power flow control. A key challenge addressed in this work is the ability to handle large voltage variations inherent to supercapacitor-based ESS. The converter is designed to accommodate voltage fluctuations on one side, ranging from zero to full charge (in the range of hundreds of kilovolts), while maintaining a constant voltage on the HVDC link side. A control strategy is developed to manage these variations efficiently, ensuring stable operation and precise power exchange. To validate the proposed approach, simulations using average model of chains of sub-modules are conducted. The results confirm that the converter respects all operational requirements, maintaining stability under dynamic conditions and effectively following the references. The findings demonstrate the feasibility of integrating large-scale supercapacitor-based ESS into HVDC grids.