Dynamic characteristics of a hybrid microgrid with inverter and non-inverter interfaced renewable energy sources: A case study

Microgrids are becoming important constituents of electric power distribution networks. Microgrids are typically comprised of both inverter interfaced (e.g. double-fed induction generator (DFIG), solar-photovoltaic (PV) system) and non-inverter interfaced (e.g. synchronous generator) renewable energy generators (REGs), hence their dynamic characteristics are significantly different from the conventional grids comprised of centralised synchronous generators. Different inherent characteristics of REGs, power dispatch levels, relative REG capacities, and external grid characteristics are some of the important features of significant interest in relation to microgrid dynamic behaviour. For this study a microgrid model was developed in DIgSILENT Power Factory based on the IEEE-13 bus system and comparative analysis has been carried out between inverter and non-inverter based REGs. The study has shown that variations in active power dispatch levels and generator relative sizing significantly influence dynamic characteristics of the microgrid hence adequate measures must be taken when designing protection schemes for microgrids. In addition, dynamic reactive power compensation and emulated frequency response schemes must be implemented in microgrids to preserve voltage and frequency stability when operating in islanded mode.