Abstract: The studies on power system oscillations were briefly reviewed. The emerging oscillation phenomena in modern power systems with increasing penetration of power electronic converters and their common characteristics were summarized. The similarities and differences among the traditional oscillations were discussed in terms of physical properties and mathematical representations. The classic Wienbridge sine-wave oscillator is used to explain the mechanism and analysis of new oscillation issues. This paper further proposed the concept of impedance network modeling and the stability criterion based on the frequency characteristics of the aggregated impedance. Their potentials of evaluating the new oscillation problems in large-scale power grids were demonstrated with actual subsynchronous oscillation incidents in wind power systems.