Fully Digital Grid Synchronization Under Harmonics and Unbalanced Conditions

Yu Bai,Baocheng Wang,Xiaoqiang Guo,Yongjian Li

doi:10.1109/access.2019.2933564

Abstract

For the grid-connected system, the unbalanced and harmonic components of three-phase grid voltage have a significant impact on the accuracy of grid synchronization. And the positive, negative sequences, harmonics, as well as dc component of the three-phase grid voltage are difficult to separate and extract in a fast and precise way. In this paper, a new fully digital phase-locked loop (FDPLL) is proposed. Compared with the existing continuous-domain methods, it is simple to implement, and able to quickly and accurately extract the positive and negative sequence components for grid synchronization. In order to verify the effectiveness and feasibility of the proposed method, the time-domain simulation is carried out. Finally, the feasibility of the proposed method is experimentally verified with a 32-bit floating-point TMS320F28335 DSP. The experimentally results verify the effectiveness of the proposed solution.

Highlights

The grid synchronization is a mandatory function for gridconnected power converter [1]–[4], especially for the faultride-through control [5], [6]
The low voltage ride through (LVRT) function is to keep the wind turbine running under short-term fault conditions of the grid
fully digital phase-locked loop (FDPLL) system to detect the magnitudes and the phase angles of the fundamental positive sequence component and fundamental negative sequence component is shown in Fig. 8, and Fig. 9, respectively

Summary

Introduction

The grid synchronization is a mandatory function for gridconnected power converter [1]–[4], especially for the faultride-through control [5], [6]. The low voltage ride through (LVRT) function is to keep the wind turbine running under short-term fault conditions of the grid. Wind turbines with LVRT capability can escape the protection action time. This can greatly reduce the number of times the power generation system is repeatedly connected to the grid in the event of a failure, and reduce the impact on the grid. The conventional PLL structure consists of three parts: phase detector, loop filter and voltage controlled oscillator [10].

Objectives

Results

Conclusion