Power flow control Methods for an ultracapacitor bidirectional converter in DC microgrids—A comparative study

Distributed generation in the form of DC microgrids has recently attracted increasing research interest. For integrating renewable energy resources and energy storage devices, such as an ultracapacitor, to the DC bus of a DC microgrid and sustain the charging and discharging states of the ultracapacitor, a bidirectional DC–DC converter is required. For the fast dynamic response of the ultracapacitor, bidirectional voltage-fed topology is preferred. But for a wide input voltage variation of the ultracapacitor, this topology exhibits a higher circulating power flow and higher conduction losses as a consequence. In this paper a comprehensive overview on several modulation methods that employed to control the power flow of the bidirectional voltage-fed DC–DC converter for the ultracapacitor applications are presented. A detailed analysis of the bidirectional converter exploring the impact of the circulating power flow interval is developed in this study. Analytical methods have been applied to establish alternative modulation methods for the bidirectional converter to improve its performance and efficiency.