State Space Modelling and Stability Analysis of AC Micro-grids for Different Configurations

Three inverter based AC micro-grid, an active load and a PQ type of inverter has been modelled in Synchronous(DQ) reference frame. The integrated model of the micro-grid with PQ inverter and active load as well as with only PQ type of inverter and R-L load has been developed. As active rectifier loads present negative incremental resistance characteristics and control loop dynamics similar to that of inverters present in the micro-grid, the various modes of the active load in the integrated system have been identified using participation analysis and their effect on the inverter states has been analysed for the micro-grid having only VSI inverters and micro-grid having PQ as well as VSI inverters. The effect of changing integrator gains for the dc voltage controller of active load on the stability has been analysed for both configurations. The effect on the stability of micro-grid was observed for different loading conditions of PQ inverter of the micro-grid.