Transient Power Control for Diesel-Generator Assistance in Electric Boat Applications Using Supercapacitors and Batteries

A freight transport hybrid electric boat (HEB) is investigated in order to improve the dynamic response of the boat during the rapid variations of the onboard load such as the acceleration/deceleration, the braking, the docking maneuvers operations, and the goods package lifting system. The propulsion architecture is based on a variable-speed diesel generator (DG) used as the main energy source, with the multiple energy storage system based on the supercapacitors (SC) and the batteries which are used in the HEB to answer the intermittent power due to a sudden load change. This solution compensates the fluctuations from the load by reducing their impacts for diesel engine. The variable-speed diesel generator is connected to the dc-bus using three-phase controlled rectifier to manage dc-bus voltage. The SC and the batteries are linked to dc-bus through two bidirectional dc/dc converters to control the high-frequency component independently to those of the average-frequency component. Two identical thrusters are, respectively, placed in the front of and the behind of the boat to emulate the propulsion operations. The HEB power demand includes the thruster's requirements and embedded appliances (elevator, package lifting system, heating system, TV, computer, and electronics device for navigation). The main contribution of this paper is focused on the HEB dynamic response improvement during the rapid variations of the load using the SC and the batteries. Other significant contributions are based on the LiFePO4-battery modeling using solartron analytical impedance spectroscopy and the load current sharing between the DG and the SC/batteries, where the high-frequency component of the load is assigned to SC due to its fast dynamic response and that of the average frequency is allocated to the batteries. The proposed energy management strategy is verified by the simulation and experimental tests in reduced scale using a specific driving cycle of the HEB for one trip.