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Abstract

As one of the key infrastructures of our modern society, the power system is of utmost importance, and meanwhile, as the largest and most complex man-made system in the world, its dynamics is very complicated and hard to grasp. The new-type power systems with renewable energy as the main body are facing many emerging problems of stability and broadband oscillation. Whether the new-type power systems can operate safely and stably is facing great risks and challenges. It is a serious problem and relevant studies can benefit from the complex system dynamical theory. Therefore, this paper first gives a basic introduction of new-type power system oscillations and further takes the synchronous-frequency oscillation (SFO) (for the oscillation at the working frequency) of the grid-forming (GFM) converter tied systems as an example. Three state-space models are established and compared to show the occurrence condition of the SFO. It is found that the transmission line dynamics, which is usually ignored in the traditional power system analysis, actually plays a dominant role in the SFO. This finding is well verified by simulations and theoretical analyses.