Impedance Analysis of Three-phase LCL-Type Grid- Connected Inverters with Adaptive PLL

In a grid-connected power system, impedance-based analysis method with considering phase-locked loop (PLL) is effective when analyzing the system stability, the stability and dynamic performance of system is considerably influenced by the performance of PLL. In this paper, adaptive PLL is applied to the grid-connected system. The advantage of adaptive PLL is that it can automatically change its parameters, Proportional parameter and integral parameter, on the basis of the real-time grid condition, so that can improve the system stability and has limited influence on the dynamic performance of the grid- connected system. This paper analyzes the frequency characteristic of typical PLL, and the effect of changing parameters. The influence of adaptive PLL on the stability of grid-connected system is analyzed in the impedance modelling. Based on three-phase LCL-type grid-connected inverters, the output impedance model with adaptive PLL is built by using harmonic linearization. And the Nyquist stability criterion is adopted to analyze the system stability. Finally, simulation verification demonstrates the correctness and effectiveness of the adaptive PLL.