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Design of an Alternative Frequency Controller for Hydropower Stations: Reducing the 60-second Floating in the Grid Frequency of the Nordic Power System
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
2014 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

A periodic oscillation in the grid frequency of the Nordic power system has been observed. The oscillations, also denoted as a floating, have periods of about 60 to 90 seconds. The reason for the floating is not fully known, and the strength of the floating has been increasing during the last years. It is assumed that the floating causes an undesired wear of the systems frequency control equipment.

The aim of the study was to research the possibility of a new control structure in primary frequency controlling hydropower units. The purpose of the new modified control structure was to dampen the grid frequency floating. The modified design of the controller was conditioned to be implemented in a smaller fraction of all regulating hydropower stations in the Nordic power system. This smaller fraction has here been assumed to 10 %.

The new structure of the modified controller was designed as a leadlag-filter, where a shape was assumed as to give the filter high energy in the frequency range of focus. The parameters of the leadlag-filter were determined according to a set of criteria, including damping ability, stability margins and preconditions on the control signals from the modified system.

The study showed that a leadlag-filter could be constructed so that a periodic grid frequency floating with periods of 60-90 seconds would be significantly reduced in amplitude. The reduction of the floating did not necessarily require more generated power compared to the current system, though the modified plants did deliver most of the power. Both reduction of the amplitude of the floating and amount of required power depended on the amplitude and frequency of the disturbance causing the floating.

Place, publisher, year, edition, pages
2014. , 73 p.
UPTEC STS, ISSN 1650-8319 ; 14027
Keyword [en]
hydropower, frequency controller, frequency floating, lead lag
National Category
Control Engineering
URN: urn:nbn:se:uu:diva-231165OAI: diva2:743757
External cooperation
Vattenfall R&D
Educational program
Systems in Technology and Society Programme
Available from: 2014-09-05 Created: 2014-09-05 Last updated: 2014-09-05Bibliographically approved

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