A Modified DPC Switching Technique Based on Optimal Transition Route for of 3L-NPC Converters

This letter presents a modified switching technique for a three-level neutral-point-clamped converters controlled by direct power control (DPC). The proposed switching technique avoids the hard state transition of each phase module as well as reduces the overall switching frequency. For any phase module, it inserts sequence of vectors to avoid the direct transition from positive to negative state and vice versa. The proposed vector sequence is called optimal transition route (OTR). The OTR technique optimizes the route between the present and the next requested vector to avoid the hard transition of any module. The proposed technique not only avoids the risk of damaging the semiconductor switches, but also minimizes the switching frequency resulted in reducing the switching losses. As a result, the reliability and the overall efficiency of the converter is increased. The obtained results confirm its applicability for medium-and high-power grid-connected converters controlled by the DPC method.