Feedback and control cascade using seven - Level NPC voltage source inverter

In this paper, the authors present a study of the stability problem of the input DC voltages of the seven-level neutral point clamping (NPC) voltage source inverter (VSI). In the first part, a knowledge model of this converter isdeveloped by using connection functions. In the second part, The authors propose a PWM strategy which uses six bipolar carriers to control the converter. In this part, The inverter is fed by constant input DC voltages. In the last part of the paper, the authors study the stability problem of the input DC voltages of the inverter. Thus, a cascade is studied constituted by three two-level PWM rectifiers - clamping bridge - seven-level NPC VSI. The obtained results show that the input DC voltages of the inverter are not stable. To improve the performances of the proposed cascade and stabilize the input DC voltages, the authors propose in this paper a solution which uses a linear feedback control of this cascade. This study allows to find a solution for the instability problem of the input DC voltages of the inverter. The results obtained with this solution confirm a good performance of the system.