Coordinated Control of Electric Tugboats Considering Inductive Power Transfer for Better Fuel Efficiency

Developments in the shipping industry have necessitated the use of numerous tugboats at harbors for high revenue growth. Over the time, electrification has gained significant potential in transport sector in view of meeting the strict emission norms. Lately, the tugboats are powered with diesel electric generators and energy storage systems to meet its propulsion and auxiliary loads. Optimal use of power sources leads to have better fuel use efficiency with reduced footprint of greenhouse gases. This paper presents an optimization technique for scheduling available power sources to meet onboard load demand. Furthermore, to transfer surplus electric power available in an electric marine vessel to the tugboats in operation nearby, the concept of wireless inductive power transfer (WIPT) is proposed for contactless charging and discharging of tugboat batteries. In addition, doubly fed induction machine (DFIM) as variable speed generator is considered in this paper for tugboat power generation in the interest of better operational efficiency at part load operation. From the test results, it is observed that the tugboat with 50 kWh battery storage system offers 21.4% of fuel saving and 25.5% of fuel saving with proposed WIPT, when compared with conventional tugboat. Further, an additional 2.6% of fuel saving is achieved by adopting DFIM for tugboat power generation.