Control of Parallel Inverter-Interfaced Distributed Energy Resources

Due to the rapid increase in global energy consumption and the diminishing of fossil fuels, the customer demand for new generation capacities and efficient energy production, delivery and utilization keeps rising. Utilizing distributed generation, renewable energy and energy storage can potentially solve such problems as energy shortage and global warming. A promising structure to interconnect these distributed energy resources is the microgrid paradigm. A microgrid comprises a variety of inverter-interfaced distributed energy resources such as fuel cells, photovoltaic arrays, microturbines, wind-turbine generators, energy storage devices (i.e., batteries, supercapacitors, etc.) and controllable loads, offering considerable control flexibility. These systems can be connected with the power grid. They can be also operated isolated from the main grid in case of disturbances or faults, which are controlled by the microgrid central controller. The key point is to control the parallel inverters so that they can work well to achieve high performances in the microgrid. This paper presents a new control method for power sharing among the parallel inverter-interfaced distributed energy resources. The proposed control method is tested in four typical scenarios: (1) three inverters switch from grid-connected mode to isolated mode; (1) three inverters switch from isolated mode to grid-connected mode; (3) three-inverter operation switched to two inverter operation in the isolated mode; and (4) two inverter operation switches to three inverter operation in the isolated mode. Simulation results suggest that this control method can make the parallel-connected inverters work well and will increase the microgrid stability.