Analysis of November 21, 2021, Kaua`i Island Power System 18-20 Hz Oscillations

This letter discusses the 18-20 Hz oscillation event at 05:30 am on November 21, 2021, in Kauai's power system following the trip of an oil power plant. As far as the authors are aware, this is the first report of a transmission system-wide subsynchronous oscillation driven by inverter-based resources (though the system in question is relatively small). In this letter, we leverage two data-based methods-the dissipating energy flow method and the sub/super-synchronous power flow method-to locate the sources of the oscillation. Also, we build an electromagnetic transient model of the Kauai power system and replay the 18-20 Hz oscillation. Finally, we propose two mitigation methods and validate their effectiveness via numerical simulation.