Simulation-Based Ship Hybrid Power System Concept Studies and Performance Analyses
Doctoral thesis
Permanent lenke
https://hdl.handle.net/11250/3005104Utgivelsesdato
2022Metadata
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- Institutt for marin teknikk [3397]
Sammendrag
The stricter regulations for emissions reduction and energy efficiency improvement are driving the maritime industries towards implementing greener and more energy-efficient solutions, one of which is a battery-based hybrid power system. Including a battery into the power system also enhances flexibility due to lowor zero-emission operation, redundancy, and power smoothing in the ship power system. However, it also increases the system complexity as it requires additional power conversion, control and safety systems, and an advanced energy management system. In addition, the performance of battery hybrid power systems in different power system architectures and various ship types requires investigation to identify the effect of battery hybridization in ship power systems.
Modeling and simulation are widely used methodologies for studies in engineering fields, mainly for the design, analysis, testing, and training of new and complex systems. Therefore, this work aims to study ship hybrid power systems and analyze their performance based on modeling and simulation. However, modeling a complex system, such as a ship hybrid power system, requires considerable time. On the other hand, the required complexity or detailing, also known as model fidelity, of the models differs with the purpose of the simulation.
This work mainly contributes by developing an energy-based dynamic model for the DC hybrid power system and analyzing the performance of battery-based ship hybrid power systems. Firstly, this work develops a dynamic model using an energy-based bond graph modeling methodology and presents its applications to study different realistic operational scenarios. Secondly, the work demonstrates a co-simulation approach to establishing a hybrid power system model. Thirdly, the work provides a system energy efficiency model applicable for the performance analysis in ship power systems, such as evaluation and comparisons using different power system architectures and high-level control strategies. Lastly, the work compares the fuel efficiency and emissions of a battery hybrid and a conventional power system in different ships types.
A DC hybrid power system model is established by integrating first principle-based physical component models and high-and low-level control system models using the bond graph modeling methodology. The validation of simulation results with laboratory data shows that the model is able to represent the system realistically. The developed system model is then applied to study various what-if scenarios in ship hybrid power systems, such as load change, bus-tie breaker operation, and component failure conditions.
Although the developed system model for the studied configuration simulates faster than in real-time, its development from scratch is time-consuming. Therefore, a hybrid power system model is established by assembling the subsystem modules in an open simulation platform (OSP) to demonstrate an efficient system model development through the co-simulation approach. The co-simulation applications like real-time virtual testing and model changeability for varying model fidelity are presented using the established hybrid power system model.
A system efficiency model is established using component efficiency models to evaluate the energy efficiency of a DC hybrid power system. It is also used to study the effect of different high-level control strategies on system efficiency. The system efficiency model is further extended to a cruise ship configuration to compare and analyze the efficiency in AC, fixed speed DC, and variable speed DC power system architectures. It shows that the variable speed DC hybrid power system is the most efficient than fixed speed DC and AC systems for the implemented control algorithm. In addition, the energy efficiency of the hybrid power system is improved than the conventional power system in all studied power system architectures, although the battery is charged onboard.
The effect of battery hybridization on fuel efficiency and CO2 and NOx emissions in four different ship types are investigated and analyzed. The investigation shows that battery hybridization of existing ship power systems improves fuel efficiency while reducing emissions. In addition, it also indicates that a battery system could replace at least one diesel generator in all the studied ship types for the considered capacities. Further, a brief techno-economic analysis of the battery hybrid system is performed to analyze the required space, weight, and cost for diesel generators and battery systems. The analysis showed that the required space, weight, and cost of the considered battery system are less than those of a diesel generator.
Finally, the developed energy-based model provides the basis to study various hybrid power system configurations and different operational, design, testing, or training scenarios. Similarly, the performance analysis of battery hybrid power systems, such as the operational efficiency and emissions, guides the maritime industries to select suitable energy carriers and power systems architectures.