Improving the Efficiency of the DAB Converter of an On-board EV Charger Using Different Modulation Techniques

Electric vehicles (EV) can act as distributed energy storage and provide ancillary services to the grid. For this purpose, a high-efficiency operation of the interfacing converter is desired over the entire power and voltage range. In this paper, firstly, a design procedure is outlined for the dual active bridge (DAB) stage of an on-board EV charger considering the prevalent charging standards and the ratings of the EVs. Thereafter, a comparison of three modulation techniques (single phase shift, dual phase shift and extended phase shift modulation) as applied to the DAB stage has been performed. The comparison study demonstrated that these techniques perform differently in various zones of operation. It is further shown that an overall gain in efficiency can be attained by changing between the modulation techniques depending on the operating point of the converter. Finally, based on these observations, the suitability of these techniques for different power-based and energy-based ancillary services has been discussed.