I. Introduction
The operation of a micro grid in isolated mode must include power control methods so the load is shared among the power sources [1], [2]. Power converters, or simply converters, operating in a microgrid can form or follow the grid voltage. For the first case, the voltage magnitude and frequency may be constant or a droop-based synchronization algorithm can adjust magnitude and frequency according to the converter power. For the latter, a different synchronization algorithm is required so the converter follows the voltage at its point of coupling. Phase Locked Loop (PLL) schemes are commonly used to estimate frequency and phase from voltage observations and to provide synchronization [3]–[5]. The phase estimation creates the synchronous reference frame (SRF) in which the current control operates.