Impedance analysis method has been widely used in the sub-synchronous oscillation of power systems integrated with large scale renewable energy connected to the grid. However

for the renewable energy and thermal power bundled system

the current methods still have adaptability problems in the modeling of electromechanical coupling components. An impedance-based method based on state space models(IMBSM)is proposed to aim at sub-synchronous oscillation studies. The dynamic characteristics of non-electric components coupled to the electrical components are modeled in the form of admittance functions. In order to cooperate with the IMBSM

a new criterion for series resonance is presented

it computes resonance frequency by the apparent resonance points in source and grid subsystem. The IMBSM not only contains eigenvalues

which are vital for system analysis

but also has more accuracy over frequency scan method. In the end

the IEEE first benchmark model is used to demonstrate the accuracy and feasibility

concerning the method and criterion proposed above.