Analysis and design of an active power filter for balancing unbalanced loads

An active power filter is proposed for balancing unbalanced loads. A three-phase, PWM (pulse-width-modulated) AC-to-DC converter topology with inductive energy storage is controlled to continuously inject desired negative sequence currents into the distribution system to achieve balancing of continuously varying unbalanced loads. The principle of operation is as follows: the negative sequence components of the load currents are measured in magnitude and in phase and the PWM-controlled active power filter is controlled to inject currents opposite to these quantities, thereby achieving the balancing function. The operation of the proposed system and the selection of the active power filter components are discussed in detail. Experimental filter operation is verified for an unbalanced load