Design and control optimization for a hybrid vessel

In this work, a multidomain simulation model for a complex marine hybrid powertrain was developed and a control strategy was implemented to optimize the powerflow. The increasing demand for sustainable marine transportation has led to a growing interest in hybridization of marine systems. The combination of traditional fossil sources together with renewable ones has a great potential impact in improving the overall system efficiency, reducing emissions and fuel consumption. Owing to the availability of a reversible energy storage system (usually a combination of batteries and super-capacitors) and one or more electrical motors that can support the thermal engine, hybrids can operate with greater flexibility. Therefore, hybrid powertrains can optimize power generation and utilization, enabling reduced fuel consumption, emissions and lower operating costs over the long term. This thesis work is organized in two main sections. In the first section, an existing hybrid ferry has been modelled using a multidomain simulation software (AVL Cruise M). The vessel has a complex diesel-electric powertrain with a hybrid energy storage system, and includes two Diesel engines, two electric motor/generators, a lithium-ion battery pack and a hydrogen powered fuel cell. Models were developed for all the relevant components, and they were characterized using experimental data provided by the powertrain’s manufacturer. The models were then assembled in a system-level model, enabling the analysis of all relevant energetic flows as well as the interactions within the vessel during a typical operational mission. In the second section, an advanced control strategy was investigated to optimize the powertrain’s performance and minimize both fuel and hydrogen consumption. Using optimization-based methods, a causal energy management strategy was developed to control the powerflows and operating points of the engines, the fuel cell and the battery, ensuring that the propulsive and accessory loads are met as well as enforcing other constraints that are required for correct and safe operation of each component. To evaluate and optimize the strategy, a multi-objective cost function was developed that aims to minimize the operational cost associated to hydrogen and diesel fuel consumption. The developed model can be used to investigate the effectiveness of the hybrid powertrain and identify strengths and weaknesses from an energetic perspective. Furthermore, the proposed control strategy can serve as a first step towards the implementation of a real-time capable optimized control strategy. The developed topic and methods are of great relevance with respect to emission compliance and the achievement of sustainability goals, including social benefits for human and planet such as the improvement of air quality in coastal areas and the reduction of noise, protecting people and marine ecosystems.