Stability and power quality issues in microgrids under weather disturbances: An implementation to the Kythnos island power system

Abstract

In this paper, a stability study of Kythnos island power system was investigated under power generation deviation due to solar insolation variations measured from ground and Earth observation. The system was tested under different disturbances, like a sudden shadowing of the photovoltaic generators due to cloudiness moving at a speed of 20km/h. It was also assumed that the dimensions of the cloud were long enough in order to cover the island. This results to a successive reduction of the PV generated power. Two other disturbances for a 24h simulation were taken from real meteorological data, one from ground measurements and the other based on satellite derived irradiance data. From the simulation results of the first disturbance, it is shown that the system is generally stable for penetration level lower than 50% while it becomes unstable at higher levels due to insufficient spinning reserve. Additionally, the time interval of the shadowing effect over the island was slow enough in order to cope with it. For the second two disturbances from real weather data, the system is operating very close to the limits for high PV penetration rates. To optimize operation a satellite based nowcasting and short-term forecasting could be used. A 15 min advance notice, that cloud cover is eminent, would be adequate to start up the back up systems and avoid instability or black out events. Such a strategy allows reserve need reductions in clear sky cases as changes in weather conditions can be predicted early enough in advance.