The Dual Active Bridge (DAB) converter is an attractive topology for modern Auxiliary Power Supplies (APS) in DC railway for its high efficiency as well as its bidirectional and isolation features. However, large parameter variations of the supply conditions result in a degraded power density when conventional Single-Phase-Shift (SPS) modulation is used. In this context, a simple control structure that achieves active damping with Triple-Phase-Shift (TPS) modulation is proposed. A small signal model of the DC railway line, filter and DAB converter is derived. Sensitivity of the control structure to variations in terms of supply voltage, output power, modulation mode and train position is investigated. Moreover, an input controller is designed to ensure stability over the whole operating range with minimal degradation of the output voltage regulation. The proposed control structure is simulated for validation considering large signal variations and power losses. Consequently, stability along with enhanced power density are reached with low complexity for DC railway APS.