A Comprehensive Synthesis of Frequency Stability in Isolated AC Microgrids

Conventional power grids consist predominantly of traditional power generation assets and sources such as oil, coal, and gas power plants. Nowadays power grids are rapidly developing towards an increasing share of power generation from renewable energy sources such as wind, solar power and fuel cells. These new assets need power electronic converters to be connected to the main grid. With this increasing trend in using inverter-based power generation equipment inverters will play a crucial role in regulation and stability of grids in the future. The management of stability in modern power grids is based on a wealth of experience and knowledge accumulated over decades of research, experimentation, and practical application. In particular, this expertise includes a deep understanding of the physical properties of large synchronous generators, which have played a critical role in maintaining grid's stability and reliability. In future grids, energy sources are mainly photovoltaic and wind energy feed, which are connected to the grid through power electronic equipment and therefore do not provide any additional inertia to the grid. Hence, the stability turns out to be a serious problem, as the power system may lose its stability under slight perturbation, e.g., start-up or shut down of a diesel generator. Therefore, new control methods or new combinations of control methods need to be considered. This paper offers important perspectives on the present state and future trends of frequency stability in AC microgrids and power systems.