In recent years, microgrids (MGs) and related technologies in Japan have advanced dramatically. On the other hand, although Japan is one of the world's leading maritime nations, the use of ocean energy as a power source for MGs is not aggressive. In addition, there are a few cases of MGs involving the marine industry and/or the fishing industry. In this article, “marine microgrids” which integrate marine energy and marine industries and the related latest trends are introduced. Especially, ship microgrids, aquaculture microgrids and port microgrids are rapidly growing up today and explained in this article.

Single-phase loads and photovoltaic generation cause three-phase imbalance in distribution systems, and prospective growth of normal chargers of electric vehicles may even increase the imbalance. The analysis of such unbalanced systems requires the three-phase power-flow calculation. Since existing methods require the admittance matrices of three-phase transformers, they must be derived for all possible winding connection patterns in advance to its computer-code implementation. This paper proposes a three-phase power-flow calculation method which formulates circuit equations using the modified nodal analysis, making it possible to automatically handle any winding connection. The power-flow constraints are then embedded into the circuit equations using a fixed-point iteration. Newton-Raphson, backward/forward sweep and fixed-point iteration methods are the existing three categories of solution methods. Newton-Raphson methods may show convergence problems due to the high R/X ratios of distribution lines. Backward/forward sweep methods cannot be used, because loops are temporarily formed in a distribution system during circuit switching. These justify the use of a fixed-point iteration. In this paper, the proposed method is validated by practical examples.

Under the spread of PV power system, abnormal sign detection of a PV module has been getting more necessary in terms of the evaluation of its influence to power grid and the maintenance of PV power plant. In the previous study, we introduced an abnormal sign detection method of PV power system combining output power region window and unsupervised machine learning method which uses only output voltage and current of the system. In this study, we made a comparative study of plural different machine learning model and revised the composition of feature quantities in order to improve the accuracy of abnormality detection.

Experiments on power generation were conducted under the open-circuit condition to validate theoretical analyses on the power generation characteristics of a co-axial MHD energy conversion device. Considering distribution of externally applied magnetic field and the electromotive force induced by the rotation of the conductive inner cylinder, the results show that the experimental open-circuit voltage was lower than the theoretical one for the wide channel width, whereas the experimental open-circuit voltage was higher than the theoretical one for the narrow channel width. The inclination of the inner cylinder might cause the decrease in effective radial ratio.