Power system even harmonics and power quality indices

This article deals with the even harmonic components (especially second harmonic components) in power system voltages and currents. The power system even harmonic components can be generated from semi-controlled three-phase rectifiers and dc-biased transformers. Those components cause unequal positive and negative peak values, which are called waveform asymmetry. Waveform asymmetries have a harmful impact on the loads sensitive to voltage or current peaks. The usual power quality indices (e.g., total harmonic distortion, telephone inference factor) are well defined for even harmonics. However none of those indices can capture the waveform asymmetry. Total even harmonic distortion (TEHD) is proposed to consider the special effect of even harmonics. A new index, asymmetry factor (AF), is proposed for the waveform asymmetry. The difference between the AF and the crest factor (CF) is clarified. Simulation and laboratory results are reported.