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.

I. Introduction

IN grid connected systems, a critical component of the converter's control system is the phase-locked loop (PLL) that generates the grid voltage's frequency and phase angle for the control to synchronize the output to [1] [2] [3] [4] [5] [6]. Estimated frequency, , and phase angle, , of the grid voltage by the PLL can be used not only for control and signal generation, through synthesis or transformations, but also in protection to detect when the converter has entered an islanded mode.