Evaluation of Harmonic Distortion under Unbalanced Supply Conditions

This paper presents a detailed study on the effect of power system voltage unbalance on the harmonics injected by a ac-dc rectifier load. This study gives an insight about the role of sequence voltage components in voltage unbalance analysis. The simulations are carried out in time domain and the frequency spectra of the distorted waveform (input and output) are obtained using fast Fourier transform (FFT). The variation of different characteristic and non-characteristic harmonics with the degree of unbalance is also investigated. A full understanding of sensitivity of the current harmonic components to different unbalance voltage operating conditions is also obtained. A new terminology named as phase total harmonic distortion unbalance factor (PTHDUF) is introduced.