Critical clearing time for isolating microgrids with inverter and synchronous based Distributed Generation

Microgrids can be viewed as a group of Distributed Generation (DG) units with the capability of operating connected or isolated from the main grid. Most of the work conducted in the area of microgrids focused on developing new control schemes that can maintain the voltage and frequency within standard limits during grid connected and islanded mode of operation. An issue of equal importance is the stability of the microgrid during system fault conditions. In this paper, the IEEE 34 bus system is equipped with a microgrid model that includes both synchronous and inverter based DG and is implemented on PSCAD/EMTDC. The results show that, depending on the DG mix and types, the critical clearing time might vary. Fast acting protective devices are required to avoid unstable microgrid operation, subsequent to system faults, for micro-grids with rotating machines. Including inverter based DG increases the critical clearing time.