Modular Power System Control for Fuel Cell-Battery Ships

Abstract

This dissertation addresses the emerging challenge of controlling electric power systems on hydrogen-powered ships equipped with fuel cells and energy storage systems. As the maritime sector faces stringent decarbonization targets, electrification, hybridization and hydrogen as a fuel have become central concepts in future ship designs. Modern shipboard power systems are becoming more complex in topology and componentry, with heterogeneous power generation and storage technologies, facing high power availability and reliability requirements. These ambitions are met with enabling technologies, most prominently DC distribution technology and power electronics converters, that lay the groundwork for a highly efficient and controllable power system. The key is thus not necessarily whether we are able to control the system but in how we should control it. Yet, existing control strategies are not designed for the real-time coordination of multiple power system components with individual characteristics, leaving untapped potential for leveraging the high controllability. Even less attention has been given to the specific challenge of coordinating multiple fuel cells and batteries in DC architectures. This topic encompasses a multitude of system-level challenges, covering aspects of power availability, stability, safety, efficiency, resilience, and scalability. Handling these requires specific attention when investigating the integration of fuel cells and energy storage systems into DC shipboard power systems. Beyond the vast discrepancy in operational characteristics between fuel cells and batteries, each component carries individual parameters, due to differences in design, rating and state-of-health. In addition, the trends of containerizing components and aiming at increased resilience shift the design paradigm from an integrated to a more modular approach. This raises the question of how modular hardware architectures can be matched with equally modular control strategies. The main challenge in the operation of complex hydrogen-based ship power systems lies in the coordination of components with different characteristics. This motivates the central research question on how to design real-time control and energy management strategies that ensure power availability and efficient resource utilization in modular, hydrogen-based DC ship power systems. The dissertation contains contributions for a comprehensive, multi-layered control framework spanning all levels of the power system hierarchy. At the lowest level, it develops an energy-based voltage stabilization method for parallel DC-DC converters, enabling adaptive power sharing among batteries and ensuring DC bus stability. Building on this, it introduces a decentralized coordination strategy for fuel cell-battery hybrid systems using virtual-impedance-based frequency decoupling, allowing components with different dynamic capabilities to share load effectively while maintaining voltage restoration and state-of-charge management. At the energy-management level, the work presents both offline and real-time optimization strategies. An offline dynamic programming approach computes globally optimal dispatch schedules that minimize hydrogen consumption and component degradation, including integer decisions such as fuel cell on-off switching. For real-time operation, the dissertation proposes a predictive, degradation-aware energy management system that uses load forecasting to optimize power allocation over medium-length horizons. The work further extends these methods to modular and distributed architectures. Through Lagrangian dual decomposition, the dissertation develops a distributed predictive energy management strategy in which each module optimizes its own power output while a coordinating agent enforces system-level feasibility. This architecture enhances scalability and resilience, enabling fault-tolerant operation and adaptation to heterogeneous component characteristics. The final contribution introduces topology-aware distributed energy management for multi-bus DC systems, allowing the energy management strategy to adapt to bus faults, switch states, and spatial distribution of loads and generators. Collectively, this dissertation delivers a modular and optimization-based control and energy management framework. It advances the field by demonstrating that scalable, resilient, and real-time coordination of multiple fuel cells and energy storage systems is feasible through a combination of adaptive functionalities, predictive optimization, and distributed architectures. Overall, the work forms a modular power system control and energy management for fuel cell-battery DC shipboard power systems. This positions the research as a significant step toward efficient and resilient, zero-emission maritime power and energy systems capable of meeting future operational and regulatory demands.