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.

This paper discusses contemporary problems concerning ship microgrids. It focuses on the role of power electronics and power quality issues, both conventional, such as voltage and frequency variations, and new issues, such as waveform distortions ensuing from the wide proliferation of power electronics in ship microgrids. The paper also contains a discussion on the provisions of the Unified Requirements of International Association of Classification Societies and other leading power quality standards in the industry, with an emphasis on Total Harmonic Distortion (THD) definition. An overview of power converters for high power applications in ships and their impact on ship networks is also given. Next, original results of various power quality phenomena recorded in ship microgrids are presented and commented on, followed by a review and recommendations for maritime microgrid modeling and signal processing methods for power quality assessment in the discussed systems. Finally, preliminary proposals for power quality control are presented.

This paper deals with the problem of estimation of voltage and current spectrum, especially harmonics, in the field of electrical power engineering. After description of hitherto used methods, a method of the combined wavelet-Fourier spectrum analysis has been proposed. The method consists in applying the wavelet transform for samples of the original signal, then using digital Fourier transform to the results for spectrum extraction. As a result, the significantly decreased number of needed multiplications is observed. A comparison of the method and fast Fourier transform, as well as the recently introduced wavelet packet decomposition, has been carried out. Finally, the results of experimental research have been shown and commented on. During research, various kinds of wavelet "mothers" and varying filter length have been taken into consideration.

Ship power systems are characterised by a comparatively high level of various power quality disturbances, such as voltage deviations, frequency deviations, voltage waveform distortions and sometimes voltage unbalance, which exert a detrimental effect on energy receivers. Among other things, power quality disturbances may cause an extraordinary increase in power losses occurring in on-board induction motors as well as ineffective utilisation of their mechanical output power. In this study, the results of empirical research which demonstrates how power quality disturbances in real ship microgrids affect induction motors are shown. The results of power quality monitoring in ship power systems from the point of view of the energy-efficient operation of induction motors are presented for various vessels and operating conditions. Recommendations concerning the revision of power quality standards and rules are elaborated to provide more energy-efficient ship operation.