An Advanced Frequency Adaptive PLL for Grid Connected Inverters Under Abnormal Grid Conditions

There has been an emerging need to diversify the utilization of distributed renewable energy sources (DRES) with grid connected inverters (GCI). A key component in the GCI's controller is the quick and precise acquisition of the phase angle of grid voltage. Phase-locked loop (PLL) controller is usually used for phase angle extraction and its performance is very crucial in abnormal grid conditions, including frequency variations, harmonic pollutions, and imbalanced grid events. Frequency adaptive PLL (FAPLL) has gained popularity due to its light computational burden, faster phase angle detection, and excellent harmonic rejection at nominal grid frequency. Unfortunately, due to spectral leakage at abnormal frequencies/harmonics, FAPLL data bears inaccuracies in both magnitude and phase angle estimation. To resolve this problem, this study proposes an advanced FAPLL (AFAPLL), which can work under abnormal frequencies or harmonics and avoid spectral leakage by implementing a variable window length phase detector, even in the presence of high harmonics in the grid voltage. Through extensive simulation results under various abnormal grid conditions, the superior performance of the AFAPLL is validated.