Adaptive grid synchronization technique for single-phase inverters in AC microgrid

Second order generalized integrator (SOGI) based phase-locked loop (PLL) technique employs two interdependent loops one for frequency and the other for phase-angle during the synchronization process in single-phase inverters and thus called the closed loop technique. During grid transients like frequency or phase jumps such synchronization technique suffers from PLL loop delay which affects the fault ride-through capability of the inverter control. Additionally, the frequency-adaptive nature of the SOGI based PLL makes it complex to implement and reduces the stability margin as well. To avoid such issues, this paper proposes a hybrid SOGI based PLL technique in which the frequency required for quadratic signal generation is provided by Teager energy operator based frequency estimation and the phase from the arctangent of the signals generated from SOGI. In the proposed technique there is no interdependent loop, thus called as open loop estimation. Moreover there is no tuning issue unlike the conventional SOGI based PLL.