Oscillation Characteristics Analysis and Equivalent Modeling of Multiple CIGs Connected to Weak Grid

The stability problem of weak grid connected converter interfaced generation (CIG) cannot be ignored. For multiple weak grid connected CIGs with different parameters, the system oscillation characteristics and equivalence methods still need to be further studied. This paper first discusses the oscillation characteristics when CIGs are perfectly coupled, perfectly decoupled and their general conditions respectively. Based on the Monte Caro simulation, the number of critical eigenvalues, the participation of each CIG to critical eigenvalues and the correlative parameters to participation are analyzed. Then the single-CIG and multi-CIG equivalence methods are proposed for stations containing nonidentical CIGs. The CIG parameters of a single-CIG equivalent model are identified based on the consistency of the output admittance characteristics. According to the different participations of CIGs with critical eigenvalues, the station is equivalent to a multi-CIG model. Results of large simulation samples show that the two equivalent models can both preserve the critical eigenvalues very well, and can be used for stability analysis. Furthermore, the multi-CIG equivalent model can also very well reflect the participation of CIGs in detailed models, and can be used for damping control study.