Mechanisms Causing the Occurrence of Subsynchronous Oscillations in Power Systems Containing Power Inverters: Part 2

Power semiconductor devices are increasingly more widely used in electric power systems as grid-tied inverters for renewable energy sources, interface elements for heterogeneous objects in microgrids, etc. On the one hand, the controllability of semiconductor devices makes it possible to impart more flexibility to modern power systems. But on the other hand, the use of these devices gives rise to processes and modes that have not existed previously, and which entail fundamental changes in the dynamic properties of power systems. One of such changes is the occurrence of subsynchronous oscillations associated with the mutual influence of the grid-tied inverter control system and the power grid operating and circuit conditions. The first part of the article [1] analyzes various stages of simplifying the grid-tied inverter mathematical model, which made it possible to determine unambiguously the mechanisms causing the occurrence of subsynchronous oscillations. In the second part of the article, a detailed state-space model is developed, using which it is possible to verify the results obtained from the simplified models and identify additional mechanisms causing the occurrence of subsynchronous oscillations. The results of simulation in the time domain and testing in a closed loop on the example of an industrial microcontroller have confirmed the conclusions drawn. As a result, the classification of the mechanisms causing the occurrence of subsynchronous oscillations has been formed, which reflects their causes and distinctive features.