Identification of modal interaction and small signal stability in autonomous microgrid operation

The detailed models of renewable energy resources based distributed generation (DG) unit, namely, wind energy conversion system, photovoltaic and diesel engine are presented in this study. Combination of different DG units in three microgrid (MG) structures is considered to investigate small signal stability and possible interaction between sensitive modes, particularly in autonomous mode of MG operation. Evaluation of oscillatory condition suggested that gain controller variation significantly influenced MG stability and system dynamic response. Moreover, since modal interaction potentially occurred due to gain change, it is necessary to identify the interaction accurately to ensure stable MG operation. The conventional identification method of eigen-interaction is conducted by observing the movements of engaged eigenvalues. However, the eigen-trajectories method is less sensitive to identify the occurrence of weak interaction. To provide more sensitive identification method, cross-participation factor (CPF) and modal interaction index (MII) analysis are proposed. Deviation of eigen-trajectories after approaching a particular interaction point, higher values of CPF and MII confirmed the occurrence of interactions. The presented works contribute for MGs gain setting consideration and proposing novel methodologies in identifying modal interaction.