In recent years

the large-scale integration of renewable energy sources represented by wind power and the widespread application of power electronic devices in power systems have led to the emergence of multi-frequency oscillation problems covering multiple frequency segments

which seriously threaten system stability and restrict the accommodation of renewable energy. The oscillation problems related to renewable energy integration have become one of the most popular topics in the field of wind power integration and power system stability research. It has received extensive attention from both academia and industries with many promising research results achieved to date. This paper first analyzes several typical multi-frequency oscillation events caused by large-scale wind power integration in domestic and foreign projects

then studies the multi-frequency oscillation problems

including wind turbine's shafting torsional oscillation

sub/super-synchronous oscillation and high frequency resonance. The state of the art is systematically summarized from the aspects of oscillation mechanism

analysis methods and mitigation measures

and the future research directions are explored.