Frequency deviations and generation scheduling in the nordic system

High penetration of variable generation such as wind power increases the demands on frequency control. The same applies to island operation and in particular if this involves variable generation, which is planned at the Danish island Bornholm. While it is obvious that the frequency control need to be considered, the disturbances caused to this control by the hourly dispatch of generation has received less attention and is the focus of this paper. Based on years of recorded PMU data, statistics of frequency events and analysis of frequency quality are made to demonstrate the relation between the frequency deviations and hourly scheduled generation. A simple model is given to reproduce these deterministic frequency variations. Simulations indicate that smaller system size as is typical for island operation does not necessarily increase these frequency variations provided load, generation, load response characteristic and system inertia are reduced with the same factor as compared to the large system.