A Three-Phase Voltage and Frequency Droop Control Scheme for Parallel Inverters

As the number of grid-connected distributed generation units continues to increase, it becomes more difficult to exclude these units from participating in the control of the grid voltage magnitude and frequency. Another future development might be the division of the grid in smaller microgrids, able to operate either connected to the utility grid or in island mode. In this paper a three-phase voltage and frequency droop control scheme for parallel connected inverters is described, which can be used for connecting a distributed energy source (a generator or a storage unit) to a microgrid, allowing both grid-connected and islanded operation. Another application is the control of parallel inverters in UPS systems. A detailed description of the control scheme is given. The performance of the proposed droop control scheme is verified by experimental results. Also an outlook to future work is given.