Microgrids are small-scale electricity supply networks
that have local power generation. This paper considers
a control strategy for inverter-based microsources within a microgrid.
The general control philosophy within a microgrid is that
sources must rely only on local information, yet must cooperate
with other sources. To accomplish that goal, the proposed controller
uses droop characteristics for active-power/frequency and
reactive-power/voltage. The proposed control strategy is based on
the use of a phase locked loop to measure the microgrid frequency
at the inverter terminals, and to facilitate regulation of the inverter
phase relative to the microgrid. This control strategy allows
microgrids to seamlessly transition between grid-connected and
autonomous operation, and vice versa. The controller has been
implemented in an actual microgrid that incorporated multiple
sources. The paper provides simulation results and documents
the performance of the hardware implementation.