The integration of dc power distributed systems in modern shipboard microgrids is receiving much attention recently due to their high efficiency and grid connection flexibility. These dc shipboard microgrids (dc-SMGs) are characterized by having different operating modes and large proportion of electric propulsion, some of which involves severe dynamic/transient conditions. Considering various operation modes of actual ships, this paper proposes a hierarchical coordinated control, which includes primary control level (PCL) and power management system (PMS) for the coordinated operation of the power sources in dc-SMGs. The coordination between the PCL and the PMS provides the following features: First, the PCL includes primary speed regulation (PSR) of diesel generator (DG) and primary voltage control (PVC) of dc bus. The PVC can realize the dynamic/steady load power sharing by adding the virtual impedance loop, and the PSR of DG performs the rotation speed to follow the reference. Second, the PMS includes optimal speed reference setting and secondary voltage recovery control that can realize variable-speed operation of DG according to its optimal energy efficiency characteristic and improve the power quality. The simulation results are carried out under MATLAB/Simulink to verify the effectiveness and robustness of the proposed control.
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