Improved frequency control strategies for geothermal power plants

The Icelandic transmission system has one of the highest ratios of installed capacity of geothermal power plants in the world, as it covers 25% of the total capacity. The current frequency controls of the geothermal power plants are outdated and needs to be revised in order to improve the frequency regulation of the industry-intensive power system. Consequently, the stability of the system is more vulnerable and the risk of island operation and load shedding is increased. In this thesis the frequency controls of the geothermal power plants has been analysed with both simulations and real-time measurements. The Icelandic PSS/E model was used for dynamic simulations of the system. As a result, several improvements of the governor model responses were suggested. Revised frequency control strategies based on wide area monitoring and control systems has been investigated. The results suggested that customized control strategies should be used for each of the geothermal power plants, in order to improve their active power support capability during dynamic events and to secure the system stability. Some system scenarios require more frequency regulation from the geothermal power plants while for other conditions a blocking of the regulation participation is more favourable. Finally, the results suggest that the real-time implementation of the wide-area control schemes, i.e. measurements, data processing and control outputs, should be based on a single application platform, in order to guarantee reliability and uniformity in the operation.