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A serious constraint in a multilevel inverter is the capacitor voltage-balancing problem. The unbalance of the different DC voltage sources of the nine-level neutral point clamping (NPC) voltage source inverter (VSI) constituted the major limitation for the uses of this new power converter. In order to stabilizes these DC voltages, we propose in this paper to study the cascade constituted by three phases three-level PWM rectifier-clamping bridge filter-nine-level NPC voltage source inverter (VSI). In the first part, the authors present a topology of nine-level NPC, then they propose a model of this converter and the algebraic PWM strategy to control it. Then in the second part we study the three-level PWM rectifier is controlled by a hysteresis strategy. In the last part of this paper, the authors study the stability problem of the input DC voltages of the inverter. Thus, this cascade allows improving the input voltages of the nine-level NPC inverter. For the solution, the output voltage of the rectifier is not stable. To remedy to this problem, the authors propose a solution which uses a feedback control for this cascade. This study allows finding a solution for the instability problem of the input DC voltages of the inverter. The results obtained with this solution confirm the good performances of the proposed solution. This study shows the effect of the stability of the DC voltages on the PMSM performances. The results obtained are full of promise to use the inverter in high voltage and great power applications as electrical traction.