Phase-Locked Loops using State Variable Feedback for Single-Phase Converter Systems

A crucial component of a grid-connected converter system is the phase-locked loop (PLL) that synchronizes the control to the grid voltage. Accurate, fast responding PLLs are required to provide phase angle and frequency measurements of the grid voltage for control and protection purposes. This paper proposes novel feedback mechanisms using the estimated frequency and phase in single-phase PLLs (in the stationary and rotating reference frames) which enhances performance. The estimated frequency ripple is eliminated without using low-pass filters (LPFs), and feedback terms are shown to improve the synchronization speed, by as much as 80% in some cases. Mathematical analyses, simulation, and hardware results are presented to verify the methods.