Characteristics Analysis of Three-Phase Symmetrical Phase-Locked Loop under Non-Ideal Grid Conditions

Abstract

Under weak grids, the output impedance of grid-connected inverter is coupled with the grid impedance, leading to poor quality of the grid current. To address this issue, the symmetrical phase-locked loop (PLL) has been proposed which can eliminate the frequency coupling and attribute the system model to be symmetrical. Although the system performances well under steady state, the characteristics of the inverter is unclear under non-ideal conditions at present. In this article, by investigating the inverter performance with the symmetrical PLL under different grid conditions, it is founded that both the dynamic and steady-state characteristics become worse compared to that with synchronous reference frame (SRF) PLL. The experiments validate the correctness of the theoretical analysis.