The three-level neutral-point-clamped (NPC) inverter was applied in active power filters (APFs). The three-level NPC inverter has the structure of split dc capacitors. So the existing dc neutral point can be directly utilized as the ground return in a three-phase four-wire system. DC bus voltage unbalance has been one of the major problems of three-level NPC inverters. In addition, high voltage and current stresses during switching cause higher system losses and lower efficiency. In this paper, a generalized three-level quasi-resonant dc-link (QRDCL) inverter is proposed, which has both the soft-switching and dc voltage self-balancing capabilities. The switching sequence for all the power switches in the proposed three-level QRDCL inverter is designed. The inverter is controlled by the 3-dimensional direct pulse width modulation with embedded auxiliary switches triggering. The proposed generalized three-level QRDCL inverter is applied in a three-phase four-wire APF. Simulation results and experimental results verified that the proposed system can achieve dc-link balance and switching losses reduction simultaneously. The efficiency of the proposed active power filter is improved and the high voltage stress during switching is released. © 2011 Praise Worthy Prize S.r.l. - All rights reserved.