A new cascaded multilevel converter based on NPC cells

A new converter topology, which is based on the modular use of modified Neutral Point Clamped cells and suitable to supply high-power medium-voltage ac motors, is presented. The proposed structure allows a remarkable reduction of the dc-link voltage capacitors and/or of the dc-link voltage ripple, with respect to the more conventional topology, owing to the implementation of a new devised control strategy. The new structure uses only two additional controllable switch-diode couples for each basic NPC cell, with a small increment in cost and complexity of the converter system. No impact on both the load and line side is created, to the exclusion of the improvement of the load voltage waveform.