Enslavement and control in dq synchronous frame for using a cascade multilevel NPC structure

The aim of this paper is to give a solution to unbalance problem of the input DC voltages of the nine-level NPC-VSI in dq synchronous frame. For that, we used in high voltage and great power applications, one two-level PWM current rectifier-nine-level NPC VSI cascade. In the first part, we develop a knowledge model of the nine-level NPC VSI and propose a space vector modulation of this converter using eight bipolar carriers. After that, this study shows particularly the problem of the stability of the DC voltages of the inverter. Then, we propose a solution to the problem by employed closed loop regulation using classic PI regulator mode in d-q synchronous frame. We add a clamping bridge to stabilise the multi DC input voltages of the nine-level NPC VSI. This cascade found applications in great power and high voltage fields as electrical traction.