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Oscillation instability of a DC microgrid caused by aggregation of same CPLs in parallel connection

The authors found that aggregation of same constant power loads (CPLs) in the parallel connection may possibly cause oscillation instability of a DC microgrid. In this study, they carry out analysis to reveal the mechanism about why the danger of oscillation instability may be brought about by the aggregation of CPLs in parallel connection. By assuming that the dynamic models of N CPLs in parallel connection are identical, analysis in this study proves that aggregated representation of the CPLs is equivalently comprised of N dynamically independent subsystems. Oscillation modes of aggregated CPLs may possibly move toward the right on the complex plane when the number of CPLs, N , increases. They propose a method to estimate the direction of movement of oscillation modes when N varies without having to conduct the modal solution of full-order state matrix. Thus, the proposed method can detect the danger of oscillation instability caused by aggregation of CPLs in parallel connection and estimate the maximum number of CPLs when the oscillation instability may occur. They present two examples DC microgrids with aggregated CPLs in parallel connection to evaluate the analytical conclusions. Application of the proposed method in planning the grid connection of CPLs is demonstrated.