A novel hybrid three-level NPC topology with digital driven serial connected IGBTs for medium voltage multi-MW wind power converter

In multi-MW wind power converter, the topology has important effects on the performance and efficiency of converter. Though many works have been done to improve and optimize the conventional three-level NPC topology, its performance is still affected by its own limitations in high power application. That is, its switching frequency is limited. In this paper, a novel hybrid three-level NPC topology with serial connecting IGBTs is proposed. It is a derivative of conventional three-level NPC topology. In the new topology, the outer IGBTs are replaced by two low voltage ones in serial connection, while the inner IGBTs are still high voltage ones. Thus, the proposed topology can increase the switching frequency of IGBTs without increased power losses. The increase of the switching frequency can also reduce the output filter´s size. And the adaptive digital drive is applied to achieve the voltage balance of serial connecting IGBTs. A down-scaled 3kW single phase leg is built up to validate the proposed topology and control methods.