An Analysis on Broadband Oscillation Characteristics of The Hybrid AC-DC Grid Based on Frequency Modal Analysis

With the scale of the hybrid AC-DC grid gradually expanded, the problem of broadband oscillation appears. Moreover, it has some new characteristics needing to be studied and solved urgently. Therefore, this paper analyzed the oscillation problem by using frequency modal analysis method, which provides theoretical support for determining the dominant factors of oscillation. Firstly, based on the theory of harmonic state space, a small signal impedance model reflecting the control characteristics of MMC was built. Then, combined with the equivalent model of the transmission line and the AC network, the impedance model of the hybrid AC-DC grid was established. Through the analysis of frequency-domain modal analysis (FMA), the quasi-resonant point, the dominant element and the influencing factors of the system oscillation were obtained. Finally, the model of the hybrid AC-DC grid was established in the MATLAB/Simulink platform to verify the correctness of the FMA method and the system oscillatory change law.