Modeling and optimal energy management strategy of a hybrid ferry boat for the city of Venice

Ship powertrain hybridization is receiving more attention thanks to potential benefits in terms of fuel consumption and emissions. The effectiveness of these solutions strongly depends on optimal ship and control design, taking into account the context of operation. The employment of hybrid diesel-electric ferries was identified as a solution to poor air quality in the lagoon of Venice, especially because of the critical values of NOx and HC registered in the last decades. In this thesis, an optimal energy management strategy for a series hybrid waterbus was investigated using a dynamic programming-based (DP) optimization algorithm. A simulation model was developed using a quasi-static approach for a series hybrid powertrain featuring two electric motors coupled to two propellers, three diesel-powered generator sets, and a LiFePO4 battery pack. The best optimal control problem was developed with the most desirable formulation of the control variables and applied to a typical mission. Results show 31% NOx and 15% HC pollutants reduction, with respect to the diesel-powered ferry currently used. Moreover, the strategy is flexible, enabling to target specific pollutants. Based on previous results, three real-time control strategies were developed, tested on multiple sailing cycles, and compared. The results show rule-based strategies are only 2% to 3% less efficient in terms of emissions but they are fast enough to run on typical electronic propulsion control systems. Finally, the encouraging results provide a strong incentive for Venice municipality to continue investing in the urban boat fleet renewal process, to meet emission regulations and ensure reputation integrity; as well as demonstrating a commitment to innovation and sustainability.