In this article, we examined dc microgrid-based maritime onboard power systems and outlined the need for and potential benefit of employing both smart grid technologies and the MVdc IPS for the future AES to enhance the controllability and efficiency of shipboard power systems. We introduced a series of technical outcomes from research on terrestrial dc microgrids, such as dc power architecture, the application of ESSs, hierarchical control, and different coordination methods. We also presented objective-oriented coordinated management methods and protective functions for future MVdc IPSs, which are to meet the specific need of maritime applications using methodologies from dc microgrids. In the last decade, there were several prototypes of ships on the low-voltage dc level, while, for the MVdc IPS, there are still technological challenges and de-risking studies to be performed. However, it is foreseeable that the advanced technologies from terrestrial dc microgrids are potentially applicable in the MVdc IPS of the future AES. Thus, such a combination will contribute to the implementation of high-performance MVdc IPSs for both commercial and mission-oriented vessels in the near future.

DC distribution is now becoming the major trend of future mobile power systems, such as more-electric aircrafts and ships. As dc distribution has different nature to the conventional ac system, a new design of well-structured control and management methods will be mandatory. In this paper, a shipboard power system with dc distribution and energy storage system (ESS) is picked as the study case. To meet the requirement of control and management of such a large-scale mobile power system, a hierarchical control design is proposed in this paper. In order to fully exploit the benefit of the ESS, as well as to overcome the limitation in controllability, a novel inverse-droop control method is proposed, in which the power sharing is according to the source characteristic, instead of their power rating. A frequency-division method is also proposed as an extension to the inverse-droop method for enabling a hybrid ESS and its autonomous operation. On the basis of the proposed methods, the control methods for management and voltage restoration levels are also proposed to establish a comprehensive control solution. Real-time simulations are carried out to validate the performance of the proposed control design under different operating conditions. When compared to more conventional droop-based approaches, the new proposal shows enhancement in efficiency.

DC microgrids built through a bottom-up approach are becoming popular for swarm electrification due to their scalability and resource-sharing capabilities. However, they typically require sophisticated control techniques involving communication among the distributed resources for stable and coordinated operation. In this work, we present a communication-less strategy for the decentralized control of a photovoltaic (PV)/battery-based highly distributed dc microgrid. The architecture consists of clusters of nanogrids (households), where each nanogrid can work independently along with provisions of sharing resources with the community. An adaptive I-V droop method is used, which relies on local measurements of state of charge and dc bus voltage for the coordinated power sharing among the contributing nanogrids. PV generation capability of individual nanogrids is synchronized with the grid stability conditions through a local controller, which may shift its modes of operation between maximum power point tracking mode and current control mode. The distributed architecture with the proposed decentralized control scheme enables 1) scalability and modularity in the structure, 2) higher distribution efficiency, and 3) communication-less, yet coordinated resource sharing. The efficacy of the proposed control scheme is validated for various possible power-sharing scenarios using simulations on MATLAB/Simulink and hardware-in-the-loop facilities at the Microgrid Laboratory, Aalborg University.

Ship microgrids have recently received increased attention, mainly due to the extensive use of power electronically interfaced loads and sources. Characteristics of these microgrids are similar to islanded terrestrial microgrids, except the presence of highly dynamic large loads, such as propulsion loads. The presence of such loads and sources with power-electronic converter interfaces lead to severe power quality issues in ship microgrids. Generally, these issues can be classified as voltage variations, frequency variations and waveform distortions which are commonly referred to as harmonic distortions. Amongst the solutions identified, energy storage is considered to be the most promising technology for mitigating voltage and/or frequency deviations. Passive filtering is the commonly used technology for reducing harmonic distortions, which requires bulky capacitors and inductors. Active filtering is emerging as an alternative, which could be realised even within the same interfacing converter of the energy storage system. The aim of this paper is to investigate recent developments in these areas and provide readers with a critical review on power quality issues, energy storage technologies and strategies that could be used to improve the power quality in ship microgrids. Moreover, a brief introduction to ship power system architectures is also presented in the paper.

The dc-link voltage dynamics can be directly used to synchronize grid-forming (GFM) converters with ac grids. However, such control scheme is prone to unstable low-frequency oscillations (LFO), owing to the constant-power dynamics at the dc link. This article analyzes first the small-signal stability of dc-link voltage-synchronized GFM converters, and proposes a control method for enhancing the system stability under different operating scenarios. In the approach, a q -axis voltage-feedforward control is introduced in parallel with the dc-link voltage control for the grid-synchronization purpose. The LFO problem with the conventional dc-link voltage-synchronization control is mitigated. Compared to conventional cascaded/paralleled dc-link voltage- and active power-based synchronization, the method mitigates the synchronous oscillation problem. Experimental tests are performed for the GFM converter operating in both rectifier and inverter modes and with different grid strengths. The results corroborate theoretical analyses and validate the effectiveness of the approach.

At sea, the electrical power system of a ship can be considered as an islanded microgrid. When connected to shore power at berth, the same power system acts as a grid connected microgrid or an extension of the grid. Therefore, ship microgrids show some resemblance to terrestrial microgrids. Nevertheless, due to the presence of large dynamic loads, such as electric propulsion loads, keeping the voltage and frequency within a permissible range and ensuring the continuity of supply are more challenging in ship microgrids. Moreover, with the growing demand for emission reductions and fuel efficiency improvements, alternative energy sources and energy storage technologies are becoming popular in ship microgrids. In this context, the integration of multiple energy sources and storage systems in ship microgrids requires an efficient power management system (PMS). These challenging environments and trends demand advanced control and power management solutions that are customized for ship microgrids. This paper presents a review on recent developments of control technologies and power management strategies proposed for AC ship microgrids.