Online characterization of interharmonics and harmonics of AC electric arc furnaces by multiple synchronous reference frame analysis

In this paper, a multiple synchronous reference frame (MSRF) analysis framework is developed to determine the positive- and negative-sequence components of all interharmonic and harmonic currents produced by alternating current electric arc furnace (AC EAF) installations, which can be considered as balanced but asymmetrical three-phase, three-wire loads on the power system. The aim of developing the MSRF analysis framework is two-fold; deep understanding of the EAF characteristics, and fast and accurate generation of reference signals to the controllers of the advanced technology compensation systems such as active power filters (APF), synchronous static compensators (STATCOM), energy storage systems (ESS), and etc., which may successfully compensate interharmonics, harmonics, and flicker. Online characterization of interharmonics and harmonics by MSRF analysis utilizes continuously measured line currents and line voltages on the medium voltage side of the EAF transformer at a sampling rate of 25.6 kHz per data channel. It has been shown by off-line computations that compensation of the sequence components of interharmonics and harmonics of the EAF currents obtained by the proposed framework, reduces the short term flicker values at the point of common coupling by up to ten fold. The proposed MSRF analysis framework has been successfully verified by comparing the frequency spectrums of the EAF currents with Fourier analysis results based on one-cycle sliding windows of 10-cycle duration.