Absolute Stability Analysis of Single-Phase Grid-Tied Inverters with Open-Loop Synchronization

For grid-tied inverters, rapid and accurate obtainment of real-time grid phase is the basic and important function for stable operation. Among existing grid synchronization schemes, open-loop synchronization (OLS) methods have attracted much concern in recent years due to fast response and the elimination of feedback loop. It is noted that near-term studies focus on the analysis and improvement of performance of OLS itself mainly, while the stability issue of OLS-based grid-tied inverter (OLS-GTI) under non-ideal grid conditions is not analyzed deeply. Because OLS owns a strongly nonlinear structure, it is hard to apply the linearized modelling and criterion to facilitate the investigation of OLS-GTI stability. Hence, to cope with this issue, based on Sector and Circle Criterion used for the stability analysis of nonlinear system, this study analyzes the OLS-GTI stability. Firstly, by setting the voltage and current amplitude benchmark, the bounded condition of nonlinear sector is acquired. Then, the absolute stability range of OLS-GTI is obtained by the Circle Criterion. Furthermore, the impact of non-ideal conditions and OLSGTI control parameters on the system stability are analyzed. Finally, the stability of OLS-GTI is tested. Using Sector and Circle Criterion can help judge the stability of OLS-GTI intuitively and facilitate the design of inverter under complex grid conditions.