Cost-Based Droop Scheme for Converters in Interconnected Hybrid Microgrids

Hybrid microgrids are the future of the power system as they bring the advantages of ac and dc networks under a common roof. As the power system continues to expand, hybrid microgrids will be connected together for increased reliability. One of the main concerns of such an arrangement is economical power sharing among multiple grids. This paper aims to address this issue by proposing a cost-based droop scheme for interlinking converters (ILCs). At the basic level, a novel voltage-frequency droop is presented which manages bidirectional power flow among the grids. Any change in ac grid frequency is translated into a dc bus voltage variation which allows active power flow from an underloaded to the overloaded grid. The conventional secondary control within the individual ac and dc grids is used to eliminate the inherent frequency and dc voltage deviations, restoring them to the nominal values. Economical power sharing among multiple grids is realized by embedding the incremental costs into the voltage-frequency droop and minimizing the total active power generation cost based on equal incremental cost principle. Different operational modes are discussed for interconnected grids, and simulations performed in power system computer-aided design (PSCAD) are used to confirm the validity of the scheme for each mode.