Enhanced Empirical Mode Decomposition Applied to Waveform Distortions

Abstract

With the pervading application of power electronics and other nonlinear time-varying loads and equipment in modern power systems, distortions in line voltage and current are becoming an increasingly complex issue. In tightly coupled power systems such as the integrated power system (IPS) onboard all-electric ships and islanded microgrids, the estimation and visualization of time-varying waveform distortions present an interesting research avenue [1]. Accurately estimating time-varying distorted voltage and current signals will help to determine innovative power quality indices and thresholds, equipment derating levels and adequate mitigation methods including harmonic filter design. In this context, it is no longer appropriate to use 'harmonics' to describe the higher modes of oscillations present in nonstationary and nonlinear waveform distortions. Harmonics imply stationarity and linearity among the modes of oscillations, while the focus of this chapter is on time-varying waveform distortions. Key issues specific to the problem of estimating time-varying modes in distorted line voltages and currents are: (a) distortion magnitudes are small, and typically range from 1-10% (voltage) and 10-30% (current) of the fundamental, (b) the fundamental frequency may not be constant during the observation, due to load fluctuations and system transients, (c) typical distortion frequencies of interest in electric power quality studies may lie within an octave -posing a challenge of separation. Time-Varying Waveform Distortions in Power Systems Edited by Paulo F. Ribeiro