Protection of Shipboard DC systems

Abstract

The development of shipboard DC power systems promises significant operational and economic benefits but faces major challenges in primary distribution, protection, and power scalability. As DC technology continues to mature, many aspects of shipboard implementation remain insufficiently defined to guarantee both safety and efficiency. Current regulatory standards are incomplete, and protection strategies often rely on outdated or inadequate frameworks. Unipolar and bipolar bus architectures each offer application-specific advantages, and the strategic placement of power electronics opens new possibilities for centralized and distributed switchboard designs. However, protection architectures still face limitations: breaker-based approaches rely on slow fuses, mechanical circuit breakers, or emerging solid-state circuit breakers, while power electronics–based protection, embedding protective functions within converters, remains underdeveloped. Furthermore, the low production rate of vessels and the varied power demands across applications often force designers to employ commercial off-the-shelf converters, raising challenges in modular topologies, scalability, and overall protection strategy.

This research addresses protection challenges through a multi-stage investigation into shipboard DC systems and power electronics for DC protection. First, a
use case–based categorization of short-circuit events in primary DC systems is proposed. A detailed fault inventory is compiled using a reference 5 MW superyacht model, providing simulation-based short-circuit data for diverse operational scenarios. The study contributes: (1) a comprehensive short-circuit inventory, (2) a qualitative fault categorization, and (3) design recommendations for power converters in shipboard DC systems. This work emphasizes that systematic fault classification is critical to understanding the impact of different short circuits and to guiding both protective device design and regulatory evolution.

In parallel, the thesis advances the state of the art in DC fault protection hardware. A high-speed solid-state circuit breaker (SSCB) is developed, integrating
a latching current limiter to prevent unnecessary tripping during transient overcurrents. Supported by a custom gate driver and controller, the SSCB prototype
achieves a clearing time of approximately 200 ns, substantially reducing system stress during faults. Both SPICE simulations and experimental tests confirm its
capability to properly operate under diverse fault conditions while requiring low complexity upgrades.

Finally, a proof-of-concept DC–DC converter with embedded protection is demonstrated. The proposed protection module, based on the electronic capacitor concept, is integrated into a 10 kW bidirectional LLC converter. Placed in series with the DC-link capacitor, the module significantly reduces processed power and conduction losses compared to conventional series-breaker configurations. Experimental validation confirms that the approach is compatible with fuse-based selectivity strategies while offering rapid fault isolation and reduced design complexity.

Collectively, this thesis provides a comprehensive framework, from system-level fault categorization to device-level protection design, supporting the safe and scalable adoption of shipboard DC systems. The proposed solutions and prototypes contribute to addressing essential protection challenges, favoring the widespread adoption of DC systems in various applications, by offering more efficient, compact, and safe DC systems, which ultimately play an important role in the transition of energy for transportation in general.