Challenges and opportunities for inverters in microgrids

Microgrids are local low voltage power systems that offer many advantages over grid power in terms of security, power autonomy and the ability to incorporate distributed generation, including renewable energy. In low voltage AC microgrids the use of renewable energy requires DC to AC conversion using inverters. With a large number of inverters in a microgrid, there are issues relating to their ability to support such a small power system when it is under stress. Such stress can be caused by voltage and frequency fluctuations arising from inside or outside the microgrid, or from faults. Currently, microgrids depend upon careful design and specification of their components for reliable operation. Many commercial inverters offer no more than power conversion at unity power factor. However, microgrids of the future are likely to be self configurable, and inverters have the potential to do much more, for example to help control reactive power and harmonics, or to offer ancillary services. In this paper, we provide some examples of the behavior of a group of commercial inverters in a working microgrid, and examine challenges and opportunities for these devices as microgrids increase in popularity.