A distributed secondary scheme with terminal sliding mode controller for energy storages in an islanded microgrid

Abstract

Different levels of the stored energy is the main challenge in control of the distributed energy storages (DESs) in an islanded microgrid. The conventional power-droop and the secondary distributed controllers of distributed generators (DGs) does not consider the long time-span dynamics of state of charge (SoC) of the DESs. Subsequently, the DESs with lower initial SoCs are discharged before other DESs. Besides, the SoC-droop primary control results in further deviation of the frequency of the microgrid. In this paper, the secondary control scheme is employed to share the power mismatch, match the SoCs of the DESs, and regulate the frequency and voltage of the microgrid. The proposed scheme has distributed cooperative architecture, and employs distributed terminal sliding mode controller (DTSMC) for the state regulators, and proportional controller for distributed power-sharing and SoC-matching. The proposed scheme organizes the controllable DGs, the DESs with limited SoCs, and the uncooperative DGs with unknown generation, through communicating between the neighbor cooperative DGs and DESs. Performance of the designed DTSMC is verified for the changes of communication topology, time-delays, data drop-outs, load variations, and external disturbances. DTSMC provides finite-time convergence, fast transients, and improved robustness.