Power-sharing based on open-loop synchronization of inverters in an islanded AC microgrid

Accurate and fast estimation of magnitude, frequency, and phase of the grid voltage is an essential part of the synchronization process and power-sharing control among parallel connected inverter-based AC microgrids, while running in islanded mode. Synchronization can be done using both open-loop and closed-loop estimation techniques. The conventional closed-loop synchronization technique used is Synchronous Reference Frame based Phase Locked Loop (SRF-PLL), estimates the phase angle of the grid voltage with a typical settling time of one or multiple fundamental periods. Moreover, the SRF-PLL estimates both, the frequency and phase angle of the voltage in one single loop, thus a jump in the phase angle affects the frequency estimation, which will have a negative impact on the power sharing control. To overcome these issues, this paper proposes an open loop synchronization technique based on Teager-Kaiser Energy Operator (TKEO) and Cross Energy Operator (TKCEO) to estimate the grid voltage frequency and phase angle, respectively. Presented results show that the power-sharing with energy operator based calculations gives a better response when compared to classical SRF-PLL.