Phase locked loop control of inverters in a microgrid

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.