Eigenvalue sensitivity analysis of microgrid with constant power loads

AC Microgrid (MG) consists of multiple inverters connected together and operating in a decentralized manner. Each inverter includes active power/frequency and reactive power/voltage droop control laws. These controllers ensure active and reactive power sharing among inverters without using communication link. This paper deals with stability analysis of the MG with converter interfaced loads operating as constant power loads (CPLs). A detailed mathematical model is developed for MG using small signal approximation. The developed model includes droop controllers, branch parameters and CPL. This model is applicable to MG with any interconnection structure. For simplicity, a three inverter system with mesh network is analyzed in this paper. The stability of this system is analyzed by determining the eigenvalues of the system. The effect of variation in system parameters, such as droop gains, interconnecting cable resistance, inductance and load impedance on the stability of the system is studied. Sensitivity of these parameters is analyzed using eigenvalues loci plots. To validate the results obtained from eigenvalues loci and to identify dominant parameters that affect system stability, First Order Eigenvalue Sensitivity Analysis (FOESA) is used. The simulation studies are carried out on Matlab/Simulink and results are included.