Investigation of non-linear devices modeled as a harmonic current source

Abstract

IEEE std. 519-1992 recommends that nonlinear devices can be modeled generally as a harmonic current source. However, some literatures propose that the voltage-source nonlinear devices actually behave as a harmonic voltage source. The need to verify if nonlinear devices can be treated as harmonic current sources in power system analysis and harmonic mitigation remains strong and challenging. In this paper, laboratory testing results at the drive input for both current-source and voltage-source drives are investigated. Simulations were performed using modified 6-pulse harmonic current spectrums for both voltage-source and current-source drives. Comparison between the simulation and lab testing indicates that both types of drives are harmonic current sources. Even though the voltage-source drives show relatively large harmonic current distortions at the drive input compared to the traditional harmonic current source model, but from the power systems point of view such type of drives should be treated as a harmonic current source. Field measurements for 33 voltage-source drives located in different locations of a large industrial distribution system are investigated for the further verification. Induction motors are primary loads in industrial distribution systems, and also loads of harmonic currents generated by nonlinear devices. Harmonic characteristics of induction motors are investigated using harmonic equivalent circuits, which provide theoretical explanations of nonlinear devices as suppliers of harmonic currents are harmonic current sources in nature.