Supply and Demand Control of Distributed Generators in a Microgrid for New Energy

We report the operational results of distributed generators (DGs) in a microgrid and present the effects after photovoltaic power generation (PV) systems were incorporated into the microgrid for an electric power system. The microgrid was constructed at the Expo 2005 Aichi site as part of a demonstration promoted by NEDO. A solution is needed for problems in which instability in DGs that utilize natural energy such as solar light and wind force negatively influences existing electric power systems. Consequently, we developed an energy-control system and controlled the output of the DGs to reduce fluctuations at the grid-connection point caused by unstable PV-system output. Our microgrid consisted of DGs such as PV systems, fuel cells, and NaS batteries, and these DGs were controlled by an energy-control system. We tested and then verified the practical effectiveness of installing the microgrid as follows. We found that (1) 99.5% of the power imbalance in supply and demand over a period of 30 min was within a range of +/- 3% under normal operating conditions, (2) the microgrid contributed to load leveling, (3) the energy-control system smoothed the power-flow fluctuations of PV-system output at the grid connection point, and (4) installing microgrids should help reduce additional Load Frequency Control (LFC) capacity in the future. (C) 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 169(4): 1-8, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20872