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

One of the most serious problems associated with the operation of AC/DC power converters is the generation of voltage and current harmonics. The values of these harmonics exceed limits given in the standards or recommendations and application of line side (AC) filters 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 values above limits specified in existing standards or recommendations, even if AC filter design using the usual procedures is applied. Therefore, AC filter design must include these harmonics. Such filters give "clean" networks in accordance with existing harmonic limitation standards or recommendations. However, their size and cost is much higher. An additional positive effect is in the significant improvement of power factor. The aim of this paper is to present an overall analysis of line side filter design for the two kinds of AC/DC power converters, during both transient and steady-states and under balanced and unbalanced power supply conditions.