An Informed Modulation Strategy for Stability Enhancement of DAB Converters Connected to a DC Railway Grid

Modern Isolated Bidirectional DC-DC (IBDC) converters in DC railway face large variations in terms of supply conditions. Thanks to its extensive modulation capabilities, the Dual Active Bridge (DAB) converter offers a promising solution for improving onboard resource efficiency. While various Modulation Schemes (MSs) have been developed to minimize power losses, their influence on cascaded system stability remains insufficiently addressed in the literature. This paper introduces a novel method for informed MS design, leveraging small-signal stability analysis and closed-loop input impedance modeling that fully accounts for both the MSs and controller parameters. The analysis also examines the dependence of a benchmark Active Damping (AD) strategy on the selected MS. For the first time, it is demonstrated that an uninformed application of Triple Phase Shift (TPS) modulation can result in instability, even with an AD strategy. Based on the proposed approach, a simple yet effective MS is designed to maximize the stability margin across the full range of supply voltages. The methodology is validated experimentally on a 1 kW, 50 kHz DAB converter, confirming its effectiveness and practical relevance for IBDC applications involving DC voltage variations.