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This research presents a thorough comparison of different modulation techniques employed in dual active bridge (DAB) converters. The performance of a DAB converter is essentially affected by the modulation technique and the operating point, including power level, input, and output voltages. A deep understanding of different modulations is required to achieve the highest performance in the entire operating range. Therefore, this paper focuses on comparing different modulation techniques over a DAB converter's operating span. The comparison results provide guidance to apply the correct modulation in certain working areas keeping the converter on top of its performance. Moreover, the paper proposes an optimization solution with distinct objective functions adoptable in DAB converters to reduce power loss. The proposed optimization approach outperforms the existing solutions regarding generality and simplicity. The optimization associates with the modulation techniques that include more than one degree of freedom, such as extended phase shift (EPS) and dual-phase shift (DPS). The proposed optimization and the investigated modulation techniques are evaluated in terms of the converter's efficiency, current stress, and backflow power. The evaluation is realized by the simulation study of a 10kW 800V/500V SiC-based DAB converter in PLECS software.INDEX TERMS Dual active bridge (DAB) converter, efficiency, modulation techniques, backflow power, current stress.

A short circuit fault in an AC railway supply system could have undesired consequences; including high-amplitude current flow in the power path, the rail potential rise in the fault vicinity. This paper studies the problem of the rail voltage rise in Tehran-Karaj railway system by the use of a steady state circuit model for the AC autotransformer during a phase-to-ground fault. By using this model, all the currents and voltages of the system can be easily calculated for all possible short circuit fault locations.With the help of the derived analytical model, one can also predict the possible fault locations which may cause the protection system to operate. The estimation of the system currents and voltages levels after the fault helps us to design more effective and economic protection systems and also to estimate the fault location.Transient effects are ignored in the proposed model and the equivalent system represents only the steady state model of the supply system after the fault.