Micro-grid operation of inverter based distributed generation with voltage and frequency dependent loads

Distribution systems are experiencing increasing penetration of distributed generation (DG). One attractive option is to use the available DG capacity during utility outages by forming planned micro-grids. Load sharing among different DG, during micro-grid operation, could be accomplished by equipping each DG with a P-f and Q-V droop characteristic. In this paper, we analyze the impact of the loads´ voltage and frequency dependence on the micro-grid´s frequency and voltage deviation during a planned islanding condition. The system was modeled and analyzed using PSCAD/EMTDC. The simulation results and mathematical analysis show that the load´s voltage and frequency dependence is an important factor when choosing the DG droop characteristic. The results also show that some loading conditions could lead to an unstable micro-grid operation.