Distributed Optimal Power Sharing Strategy in an Islanded Hybrid AC/DC Microgrid to Improve Efficiency

Abstract

In an islanded hybrid ac/dc microgrid (IHMG), ac and dc subgrids are connected via interlinking converters (ICs). For reliable operation of an IHMG, achieving distributed generators' power sharing (DGPS) throughout the entire IHMG and ICs' power sharing (IPS) is the main objective in an IHMG. To improve efficiency of an IHMG, minimizing operating costs of DGs is required and thus cost-minimized DGPS needs to be achieved. Similarly, when multiple ICs operate in an IHMG, efficiency-maximized IPS can further improve the efficiency of an IHMG, as total loss of ICs can vary by the IPS ratios. Thus, this paper proposes a distributed power sharing strategy to achieve cost-minimized DGPS and efficiency-maximized IPS simultaneously, without any communication lines for DGs. Incremental cost-based droop controlled DGs and distributed controlled ICs are coordinated for cost-minimized DGPS and a distributed optimal power sharing method of ICs is proposed to achieve efficiency-maximized IPS. The proposed strategy secures both cost-minimized DGPS and efficiency-maximized IPS, with only sparse communication lines among ICs, thus resulting in a significant improvement in IHMG efficiency and reliability.