Abstract: The increasing penetration of the renewable energy has increased the risks of the sub/super synchronous oscillations in the power systems. It is critical to evaluate the oscillatory stability of the renewable power systems accurately which could help to ensure the safe and stable operation of the system. A method for evaluating the oscillatory stability of the renewable power systems based on frequency-domain modal analysis was investigated in this paper. First, the frequency-domain impedance/admittance models of the key equipment and stations are established, including the renewable power generators/stations, transmission lines, synchronous generators, transformers, etc. Second, a system-level frequency-domain network model is constructed based on the actual system topology. Third, the oscillatory stability of the renewable power system is evaluated by solving the zeros of the determinant of the loop impedance matrix or the node admittance matrix of the system. And the weak points of the system can be located based on the participated matrix of the weak oscillation mode, which provides the reference for the implementation of oscillation suppression measures. Taking the practical renewable power system in East China as an example, the oscillatory stability of the system under the changing access capacity of renewables and grid operating conditions was assessed using the frequency-domain modal analysis method. Finally, the time-domain simulation model of the actual renewable power system was built in PSCAD/EMTDC to verify the correctness of the theoretical analysis.

Key words: renewable power system, oscillatory stability, frequency-domain network, frequency-domain modal analysis, stability assessment, weak point location