Perturbation-Based Sensitivity Analysis of Slow Coherency With Variable Power System Inertia

The identification of generator coherency is crucial to design intentional controlled power system islanding. Due to high penetration of nonsynchronous generation, power system inertia changes both temporally and spatially. Thus, the dynamics in system oscillations and associated slow coherency of generators are directly affected by this. Therefore, their sensitivity deserves investigation. In this paper, the slow coherency with variable inertia is systematically discussed by incremental analysis. Specifically, the approach to study the impacts of variable inertia, based on the matrix perturbation theory, is deployed to provide the explicit eigen-solution sensitivity of slow coherency. To investigate the dependency of coherency grouping on inertia, the changing trends of eigenvector and possible alteration of coherency grouping are estimated. The unusual and abrupt alteration of slow coherency is observed in special scenarios near to modal resonance, i.e. close eigenvalue. The analysis in such scenarios was hardly found in the previous work of coherency sensitivity. Since close eigenvalue can make the traditional matrix perturbation inapplicable, the feasible perturbation in such special scenarios is proposed in this paper. The proposed approach has been thoroughly tested using the classic IEEE 118-bus system. The quantitative results are compared with those obtained analytically.