Yes, the SSO issue in the northwest US power system is a textbook case of this, although in that case IIRC the main issue was control interactions between the p

Yes, the SSO issue in the northwest US power system is a textbook case of this, although in that case IIRC the main issue was control interactions between the power system stabilizers* oscillating together and actually exchanging quite a bit of energy over long distances at a low frequency because those very low frequencies were not effectively damped (or in some cases, negatively damped). At the time, the tools available for large scale power system modelling were very rudimentary compared to what we have today. In general I don't see it as a renewable vs. conventional issue. SSO/SSR/SSCI have been around since the 1960s when PSS started to be deployed in synchronous generator excitation control systems. Rather it reflects the greater complexity in modelling involved high speed digital controls vs. physical, inertial responses that are expressed very effectively by well-known equations. As we layer on more and more controls, we don't only have to model what is going on at power frequency (50 or 60 Hz) but also at harmonic frequencies and sub-synchronous frequencies. Renewable generators just happen to depend much more heavily on complex control systems for power conversion, mimicking synchronous generator response characteristics and to marry all the components of a large renewable plant together. At the same time, we have far more powerful tools for power system simulation today that can effectively mitigate this risk, as long as engineers realize the risk is there. A good reference explaining SSO as it applies to conventional generators can be found here: http://www.cigre.org.br/archives/pptcigre/07_subsynchronous_oscillations.ppt http://www.cigre.org.br/archives/pptcigre/07_subsynchronous_... * Power system stabilizers (PSS) are a part of synchronous generator excitation control that improves dynamic stability by damping generator oscillations against the grid. However, PSS systems can actually cause additional, long-distance oscillations with other PSS systems in the frequency range of 0.1 to 1 Hz. See: https://www.wecc.org/Reliability/Power%20System%20Stabilizer%20Tuning%20Guidelines.pdf https://www.wecc.org/Reliability/Power%20System%20Stabilizer... and http://www.meppi.com/Products/GeneratorExcitationProducts/Static%20Excitation%20System/Power%20System%20Stabilizer.pdf http://www.meppi.com/Products/GeneratorExcitationProducts/St...