Enhanced Grid-Connected Phase-Locked Loop Based on a Moving Average Filter

Cong Liu,Jiayan Jiang,Zhongzheng Zhou,Jianguo Jiang

doi:10.1109/access.2019.2963362

Cong Liu, Jiayan Jiang + Show 2 more

Open Access

https://doi.org/10.1109/access.2019.2963362

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Abstract

Moving average filter (MAF)-based phase-locked loops (PLLs) have received considerable attention in recent years due to their attractive features. Indeed, they are able to completely eliminate the unwanted effect of harmonics, dc offset, and unbalanced voltages. Unfortunately, these advantages come at the cost of open-loop bandwidth reduction, which worsens the system's dynamic response. The main challenge is to estimate the phase and frequency timely and precisely from an imbalanced and distorted voltage. In addition, optimized parameter design is also a difficult issue. The main aim of this paper is to present an enhanced PLL based on a moving average filter (EMAF-PLL) and a control method with a novel compensation algorithm. The EMAF-PLL can maintain high performance even under harsh grid conditions, and the novel control method enables the designer to set the controller parameters simply and effectively. The design method compensates the PLL small-signal model to form a type-II classic system and then optimizes the control-loop design by the rules of type-II systems. Finally, experimental investigations are performed to validate the effectiveness of the EMAF-PLL. The experimental results are also presented, and comparison with conventional PLLs verifies that the dynamic performance can be significantly improved.

Highlights

Appropriate synchronization with the utility grid, when the grid voltage is affected by unwanted and severe disturbances such as voltage sags, high distortions, and frequency jumps, is an issue of high importance for almost all grid-connected power electronic equipment
MODELING OF Moving average filter (MAF)-PLLS Fig. 2 shows the control structure of MAF-phase-locked loops (PLLs), which consists of three parts: a phase detector (PD), loop filter (LF), and voltage-controlled oscillator (VCO)
Equation (16) indicates that the EMAF-PLL is a type-II classic system [26], and the dynamic response can be optimized by selecting the PI parameters as ki = 2h22 (17)

Summary

INTRODUCTION

Appropriate synchronization with the utility grid, when the grid voltage is affected by unwanted and severe disturbances such as voltage sags, high distortions, and frequency jumps, is an issue of high importance for almost all grid-connected power electronic equipment. The author has demonstrated that the MAF-PLL provides good filtering capability, which is attained at the cost of a slower dynamic response To overcome this challenge, several approaches, such as removing the in-loop MAF(s) and placing them before the input of the PLL [14], using a quasi-type-I PLL structure [15], [16], and using a hybrid type-I/type-II PLL structure [17], have been proposed in the recently published literature. Liu et al.: Enhanced Grid-Connected PLL Based on a MAF ignored, and parameter tuning based on a second-order linear system was given It is difficult for the control parameters obtained by ignoring the MAF to achieve excellent phase-locking performance. The experimental results show that the steady-state phase locking of the EMAF-PLL exhibit high accuracy, and its dynamic response speedup is significant

MAF CHARACTERISTICS MA

COMPENSATION MODULE

PI REGULATOR DESIGN

EXPERIMENTAL VERIFICATION

Findings

CONCLUSION