Coordinated Control of a Hybrid-Electric-Ferry Shipboard Microgrid

DC and dc/ac hybrid distribution and energy storage for shipboard power systems (SPSs) are becoming a major trend due to efficiency improvement, space saving, and maneuverability enhancement. This paper has taken a real hybrid-electric-ferry as a case-study to integrate battery units (BUs) to a dc bus for supplying the propulsion motors. Furthermore, two diesel generators (DGs) are connected to the ac bus to supply the hotel loads, and a bidirectional dc/ac converter with an LCL filter is responsible for the power flow between ac and dc buses. This power topology is flexible for this ferry operation in pure electrics, extended range, and shore power modes. The DC bus voltage is stabilized and its voltage ripple is limited by BUs' interleaved three-phase bidirectional dc/dc converter with its controller considering the operation states of propulsion motors. A coordinated power flow control between DGs and BUs is presented that the system frequency is fixed for the optimal operational efficiency of the diesel engines and a Q-V droop control plus a virtual impedance loop is used to make different ac bus voltages. Synchronization with shore power and the dc/ac converter is facilitated by P-f droop control. Simulation results are presented to validate the proposed control approach in different missions.