Evaluation of Current Interharmonics from AC Drives

Distortion levels on power systems have been continuously increasing due to the increasing presence of power converters. The distortion currents injected by some converters can include interharmonics as well as harmonics. The generation of interharmonics in ac-dc-ac power converters is discussed, and a method to predict levels of current interharmonics is developed. The results show that very low interharmonic levels can be expected for a well designed PWM inverter operating with linear modulation and balanced load. Interharmonics can be expected in cases when the inverter is in overmodulation or when the inverter load is unbalanced. The paper also discusses the relative effects of dc link inductance and source inductance on interharmonic propagation. Index Terms--Power converter harmonics, power quality, pulse width modulated inverter.