Study on microgrid operation modes switching based on eigenvalue analysis

The purpose of this paper is to investigate the characteristics of the switching caused by the microgrid transitions based on the eigenvalue analysis. The factors, including control parameters, line parameters and load parameters, which have impact on the eigenvalues of the two operation modes of the microgrid are studied. In addition, the parameter sensitivity analysis for the dominant eigenvalues is carried out under different load levels in two operation modes of microgrid. The results show: the line parameters and the load parameters have less impact on the stability of the microgrid system than control parameters in either the grid-connected mode or islanded mode; the parameter sensitivity of kpi, the proportional parameter of inner-loop current controller, for the dominant eigenvalue is increased after the microgrid switches from grid-connected mode to autonomous mode. This may cause the microgrid instable in the autonomous mode even if transition from a stable grid-connected mode. Therefore, the parameter kpi should be adjusted to a suitable value to maintain the microgrid stable during the switching, once the island state of microgrid is detected. By comparing the change of the eigenvalues distribution in the modes switching of micro-grid, some smooth-switching control strategies are proposed. Finally several time-domain simulations are present to verify the above result.