Evaluation of Phase-Locked Loop Stability Considering Electromagnetic Transient Process

Abstract

Grid-following converters may experience loss of synchronization, especially when power system becomes weak or grid fault occurs. So far, it has been found that this phenomenon is associated with Phase-Locked Loop (PLL) dynamics and several methods to analyze such issues have been proposed. However, it seems that the impact of electromagnetic transient process caused by converter current variation or grid voltage drop is not well investigated in these methods. In this article, a systematic method considering such electromagnetic transients for PLL stability assessment is presented. According to the proposed approach, the PLL performance involving the electromagnetic transient process is derived by using differential equations in time domain. Moreover, based on the nonlinear system theory, a scheme for PLL stability evaluation is designed. The effect of the electromagnetic transients on the stability of PLL system is also discussed. The accuracy of the proposed method is validated through simulation.