In recent years, more and more evidence suggests that the global energy system is on the verge of a drastic revolution. The evolutionary development in power electronic technologies, the emerging highperformance energy storage devices, as well as the ever increasing penetration of renewable energy sources (RES) are commonly recognized as the major driven force of the revolution, the outburst of customer electronics and new kinds of household electronics is also powering this change. In this context, dc power distribution technologies have made a comeback and keep gaining a commendable increase in research interests and industrial applications. In addition, the concept of flexible and smart distribution has also been proposed, which tends to exploit distributed generation and pack the distributed RESs and local electrical loads as an independent and self-sustainable entity, namely microgrid. At present, the research of dc microgrid has investigated and developed a series of advanced methods in control, management and objective-oriented optimization, which would found the technical interface enabling the future applications in multiple industrial areas, such as smart buildings, electric vehicles, aerospace/aircraft power systems, as well as maritime power systems.

DC microgrids built through 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 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 SOC 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 a) scalability and modularity in the structure, b) higher distribution efficiency, and c) 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 loop facilities at microgrid laboratory in 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.

Abstract-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 conventional AC system, new design of well-structured control and management methods will be mandatory. In this paper, shipboard power system (SPS) with DC distribution and energy storage system (ESS) is picked as 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 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 hybrid energy storage system (HESS) 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 proposed control design under different operating conditions. When compared to more conventional droop based approaches, the new proposal show enhancement in efficiency.Index Terms-Shipboard power system, DC distribution, energy storage, hierarchical control, more-electric ship, islanded microgrid.

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.

He will join in Energy and Power Group, Oxford University, UK, as a postdoctoral researcher in November 2018. His research interests include multi-port converter design, distributed controller for AC and DC microgrid. He received an outstanding presentation

In DC microgrids, virtual resistance based droop control is broadly used as the fundamental coordination method. As the virtual resistance guarantees load sharing effect in steady states, the output admittance determines the dynamic response of converters in transient states, which is critical in stability analysis and system design. So far, two different approaches of droop control (i.e. V-I droop and I-V droop) are proposed. Although they can achieve the same steady-state power sharing effect and fully compliable with each other, the output characteristics are not the same due to significant difference in control architecture. In this paper, a comparative admittance-based analysis is carried out between these two approaches. State-space models and more general analytical models are established to derive the output admittance of droop-controlled converter in DC microgrids. Simulations and impedance measurement is carried out using PLECS to validate the analytical results.

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