Isolated Y-Connected Multiport Converter for Interconnecting DC Systems with the AC Grid

With the increasing adoption of dc-based energy sources, storage systems, and loads, there is a growing need for efficient and flexible power conversion interfaces between dc systems and the ac grid. This paper presents an isolated multiport converter designed to interconnect multiple dc systems with the ac grid. The proposed converter provides galvanic isolation among different ports, mitigating leakage currents, enabling flexibility in selecting grounding schemes for both ac and dc sides, and facilitating seamless integration of a wide range of dc voltage levels. The operation principles are discussed, where the primary ac-side is modulated with a fixed duty cycle, while the two secondary dc-sides employ space vector modulation to match the voltage of the primary side of the multi-terminal transformer. Power flow among different ports is controlled using phase-shift modulation. To ensure robust and independent control of each port, a decoupling control matrix, derived from a linearized power flow model, is incorporated into the control system. The converter's performance is demonstrated through simulation results, where it is designed to interlink 400 V dc systems with the ac grid.