Unbalanced AC/DC converter AC filter design in transient and steady state

Abstract

One of the most serious problem associated with operation of AC/DC converters is generation of voltage and current harmonics. The values of harmonics exceed limits given in the standards or recommendations. Application of line side (AC) filter is necessary. The usual methods of AC filter design are based on steady state performance and balanced power supply. However, harmonics during transient states with unbalanced power supply significantly increase their levels. In such cases, they can reach the values that are above limits specified in existing standards or recommendation, even if AC filter designed by usual procedure is applied. Therefore, AC filter design must include these harmonics. Such filter gives 'clean' network in accordance with existing harmonic limitation standards or recommendations. However, its size and cost is much higher. Additional positive effect is in significant improvement of power factor. The aim of the paper is to present an overall analysis of line side filter design for the two kinds of AC/DC converters, during both transient and steady states and in balanced and unbalanced power supply conditions.