Inter-area Resonance Phenomenon in the Nordic Power System Excited by Forced Oscillations

Power system stability is a well-known matter in power engineering, and it is crucial in ensuring the reliable power systems operations. One phenomenon to cause power system instability is known to be low frequency inter-area oscillations. In recent years, transmission system operators have identified significant amplifications in the inter-area modes, excited by forced oscillations. The phenomenon is recognized as an inter-area resonance.
The research studied inter-area resonance phenomenon, excited by the interactions of inter-area oscillation modes and forced oscillations. To specify, the research focused on the resonance phenomenon regarding the 0.3–0.4 Hz inter-area mode between Southern Finland and Southern Sweden. The mode and its damping are known to cause restrictions in the transmission capacity between Finland and the rest of Nordic countries.
The objective was to determine which properties of a forced oscillation have the most prominent resonance effect on the inter-area mode. Also, it was studied, if the operational conditions of the Nordic power system have an effect on the phenomenon.
The research was implemented by simulating a model of the Nordic power system. Based on the generated data, the resulted amplification in the inter-area mode were determined. The effects of certain forced oscillation properties regarding the inter-area resonance were examined by these amplifications. The results were analyzed in a comparison with the prior research.
The objective of the research was achieved. The findings suggested that inter-area resonance is a phenomenon with numerous factors affecting it. However, the most crucial are the damping of the inter-area mode resulting from the power flow situation, and the frequency and location of the forced oscillation. The findings also showed similarities with the prior research but also, to some extent challenge certain preconceptions.