Two-Layer Control Scheme for Maintaining the Frequency and the Optimal Economic Operation of Hybrid AC/DC Microgrids

In this paper, a two-layer control scheme is proposed to improve the optimal economic operation of hybrid ac/dc microgrids. The proposed scheme consists of the lower layer representing a continuous dynamic control model with a solution that is analogous to the iterative solution of a decentralized economic dispatch problem for ac and dc sections. The upper layer, which includes primary, secondary, and tertiary coordinations in interlinking converters (ICs), regulates power exchanges between the two sections. Local controllers in ac and dc sections are coordinated to regulate the microgrid frequency and voltages while maintaining the economic dispatch in each section. The microgrid master control implemented in the tertiary IC coordination will optimize power exchanges between the two sections. The difference in incremental costs of ac and dc sections is utilized in the tertiary IC coordination for reducing computation and communication requirements of the optimal solution. The effectiveness of the proposed control scheme is verified by applying time-domain simulations in PSCAD/EMTDC to the optimal operation of a hybrid ac/dc microgrid.