Multiport Converter Design for Meshed DC Microgrids

Abstract

The recent rise in power demand in data centers, driven largely by AI workloads, has exposed the limitations of conventional AC and radial DC distribution architectures, particularly the losses and added complexity introduced when each stage of voltage conversion is handled by a separate, single-purpose
converter. This thesis investigates whether a single multiport converter, designed around the operating conditions of a meshed DC microgrid, can replace this stack of point-of-load converters while preserving efficiency, redundancy, and standards compliance.

A Tier IV, 2N redundant DC data center was modeled in DCIDE as a meshed system under power-voltage droop control. Lifetime-weighted simulation across normal, degraded, and fault scenarios showed that each port of the converter spends the majority of its operating life well below rated power. This helped determine the right value that the converter ports should be sized for, rather than sizing them around their rated maximum, as is conventional. Building on this, a port-specific earthing strategy was derived against the Current/OS distribution standard, and candidate multiport converter topologies were compared using a weighted scoring framework using cost, complexity, and efficiency.

The selected topology, built around the dual active bridge (DAB) as its isolated DC-DC stage, was validated first in MATLAB Simulink using an ideal-component model with closed-loop voltage control for the two voltage-regulated ports and open-loop, fixed-phase-shift control for the current-controlled battery-interfacing port, and then in PLECS using manufacturer-derived switching-loss and thermal
models. The PLECS results showed sub-converter efficiencies above 97.5%, junction temperatures within design limits, and an overall simulated system efficiency of 98.29% against a theoretical estimate of 98.00%, validating the functionality and efficiency of the selected topology.

Beyond the data center case study, this thesis develops a transferable methodology for sizing, earthing, and selecting multiport converter topologies in meshed DC microgrids more broadly.