An Adaptive Time-Efficient Technique for Harmonic Estimation of Nonstationary Signals

Model-based parametric techniques offer many advantages over conventional discrete Fourier transform-based methods for harmonic/interharmonic estimation. However, high computational requirements restrict their applications to offline analysis purpose. In this paper, an adaptive technique based on estimation of signal parameters via rotational invariance technique (ESPRIT) is proposed that optimizes the accuracy and computation time for harmonic/interharmonic estimation of stationary as well as nonstationary power supply signals. This method first estimates the order of the model (number of sinusoids present in the distorted power supply signal) and then adjusts the autocorrelation matrix dimension based on reconstruction error. The performance of the proposed method is validated on the time-varying simulated signal, measured synthetic signal, and actual voltage signal of a distribution system supplying electric arc welding load. The comparison of the results with the short-time Fourier transform and the sliding window ESPRIT techniques shows that the proposed approach considerably reduces the computational time of high-resolution ESPRIT method along with better accuracy.

I. Introduction

The present-day power system consists of substantial proportion of harmonic-generating equipment in the form of converters (e.g., uninterrupted power supply, high-voltage dc transmission, renewable energy source integration, distributed generation, etc.), controllers (e.g., flexible ac transmission systems, etc.), and nonlinear loads such as variable-speed drives, battery chargers, electric arc furnace, etc. The overall effect of these harmonic-generating devices on the system is nonstationary harmonics/interharmonics, which result in many ill effects including increased losses, protection and control malfunction, resonance, communication interference, etc. [1], [2]. The estimation of nonstationary harmonics/interharmonics with higher estimation accuracy and low computational time is essential for continuous monitoring and control of modern power systems from power quality and reliability point of view [3] because it provides fundamental basis for accessing harmonic sources in the network [4], for designing suitable solutions for mitigation and control [5], for cost effect analysis and recovery from accountable consumers [6], [7], and for trading of related ancillary services in the deregulated energy market [8]. Ukai et al. [9] have proposed global positioning system-based synchronized measurement of harmonics for monitoring over wide area network. Also, performance indices like total harmonic distortion, harmonic group, subgroups, etc., are developed, and guidelines have been framed to define allowable harmonic limits and measurement practices [2], [10]–[12].