Voltage-frequency control of an islanded microgrid using the intrinsic droop characteristics of resonant current regulators

The Distributed Generators (DGs) of an islanded microgrid must be carefully controlled to regulate voltage and frequency, and to share power evenly between the DG sources. This is normally achieved by operating the microgrid Voltage Source Inverters (VSIs) in voltage controlled mode, so that the microgrid voltages and frequency can be explicitly regulated. However, this results in the loss of direct control of the VSI current, and potentially introduces the need for communication between DG units to maintain robust coordination between DG sources. This paper presents a new approach for islanded microgrid operation, where all VSIs are operated in current regulated mode. By taking advantage of the hitherto unrecognised intrinsic droop characteristic of a PR current regulated VSI, frequency regulation, voltage regulation and power sharing can be achieved across the islanded microgrid without requiring either explicit external control or direct communication between the DG units. Simulation and experimental results are presented to verify the performance of the new approach.