System-level design optimization of a hybrid tug

Designing a new vessel is a complex multi-objective design process. It involves knowledge from different fields, like naval architecture and mechanical engineering. Assessment of an optimal design for more complex topologies than a conventional Diesel powertrain becomes more difficult due to the increased number of powertrain components and feasible combinations. The purpose of this work is to present a system-level design methodology, which speeds up the component sizing and control for a powertrain topology. This system-level design problem is formulated into the minimization of a cost function. The cost function consists of the costs of the different powertrain components together with the operational costs over a specified operational profile. For the sizing of the battery and control parameters, the use of a convex optimization algorithm ensures a global optimum is found very quickly in the search space at relatively low-computational effort. For the ON/OFF switching of the Diesel engine and the Diesel generator set, an iterative scheme using convex and mixed-integer optimization is proposed. Here, without loss of generality, the optimization case study is presented for a hybrid tug.