Enhanced Dual-Spectrum Line Interpolated FFT with Four-Term Minimal Sidelobe Cosine Window for Real-Time Harmonic Estimation in Synchrophasor Smart-Grid Technology

Helmo Kelis Morales Paredes,Venkata Sesha Samba Siva Sarma Dhanikonda,Venkata Subrahmanya Raghavendra Varaprasad Oruganti,Marcelo Godoy Simões

doi:10.3390/electronics8020191

Abstract

The proliferation of nonlinear loads and integration of renewable energy sources require attention for accurate harmonic estimation along with estimation of fundamental amplitude, phase, and frequency for protection, improving power quality, and managing power effectively in a smart distribution grid. There are currently different Windowed Interpolated Fast Fourier Transform (WIFFT) algorithms for harmonic voltage estimation, but estimation of current harmonics using WIFFT is not explored sufficiently. The existing WIFFT algorithms, when used for current harmonic estimation result in low accuracy due to spectral leakage and picket fence effect. On the other hand, Interpolated Discrete Fourier Transform (DFT) is used for synchrophasor quality metrics, but it is effective only when there are no harmonics and the fundamental frequency is constant. This paper proposes a unified solution, comprising of peak location index search (PLIS)-based Dual-Spectrum Line Interpolated Fast Fourier Transform (DSLIFFT) algorithm with 4-Term Minimal Sidelobe Cosine Window (4MSCW) for estimating both low-amplitude voltage or current harmonics and synchrophasor under variable frequency conditions for high-penetration renewable energy utility grids. The effectiveness of the proposed algorithm is validated by simulation studies and real-time experimentation using the National Instruments reconfigurable embedded system under nonlinear loading conditions.

Highlights

Accurate estimation of current and voltage harmonics, as well as real-time measurement of voltage space vectors, i.e., synchrophasors, are essential for power electronic based nonlinear loads and the integration of renewables in the modern distribution network
These methods are classified as non-parametric and parametric methods as reviewed in [5]. Parametric methods such as Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), Multiple Signal Classification (MUSIC), Kalman Filter (KF), and Prony method require the prior information of the estimation signal for modeling; otherwise, it leads to erroneous results [5,6]
The 4-Term Minimal Sidelobe Cosine Window (4MSCW) functions and its corresponding peak location index search (PLIS)-based Dual-Spectrum Line Interpolated Fast Fourier Transform (DSLIFFT) algorithm proposed in this article for harmonic and synchrophasor estimation are summarized

Summary

Introduction

Accurate estimation of current and voltage harmonics, as well as real-time measurement of voltage space vectors, i.e., synchrophasors, are essential for power electronic based nonlinear loads and the integration of renewables in the modern distribution network. For the accuracy of the estimation method, as well as the requirements of international standards [1,2,3], it is important to have a fast, accurate, and easy-to-design compensation devices. Numerous signal processing methods have been adopted for the estimation of power system harmonics [5,6]. These methods are classified as non-parametric and parametric methods as reviewed in [5]. Parametric methods such as Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), Multiple Signal Classification (MUSIC), Kalman Filter (KF), and Prony method require the prior information of the estimation signal for modeling; otherwise, it leads to erroneous results [5,6]

Methods

Results

Conclusion