Stability Analysis and Control of Two-Stage Three-Phase Photovoltaic Grid-Connected System with Phase-Locked Loop

This paper presents a small-signal model of two-stage three-phase photovoltaic grid-connected system including phase-locked loop (PLL). Using the eigenvalue analysis, the dominant oscillation mode of the system under weak grid conditions is determined and the results show that MPPT control parameters have relatively little impact on system stability. Based on the interaction between PLL and inner current loop, an additional control method is proposed to suppress the dominant oscillation mode. It is further proved by eigenvalue analysis and time domain simulation that the proposed method is correct. Then the lower limit values of the additional control coefficient under different PLL gains are given.