AC Microgrid Control Using Adaptive Synchronous Reference Frame PLL

This paper presents AC microgrid operation in grid connected and islanded mode. Accurate detection of distributed energy resources (DERs) islanding from utility grid is necessary to initiate any control action within the microgrid. In order to detect islanding occurrence, an adaptive synchronous reference frame phase locked loop (ASRF-PLL) has been utilized in this paper. This modified PLL provides stable operation in grid connected and islanded mode and maintains frequency to its nominal value. Furthermore, droop control for frequency and voltage amplitude restoration under different islanding scenarios has been discussed. Islanding operations studied in this paper are independent synchronous generator (SG), parallel inverters feeding the local loads, and hybrid islanding including both SG and inverter based DERs. Simulation results are presented for aforementioned islanding scenarios which validate the effectiveness of proposed islanding detection algorithm and control techniques to keep voltage amplitude and frequency within prescribed limits.