Study and control of two two-level PWM rectifier—clamping bridge-seven-level NPC VSI cascade: Application to PMSM speed control

摘要

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, they develop a knowledge model of this converter by using connection functions. In the second part, the authors propose a PWM strategy which uses six bipolar carriers to control this converter. In this part, the inverter is fed by constant input DC voltages. In the last part of this paper, the authors study the stability problem of the input DC voltages of the inverter. Thus, they study a cascade made up of two two-level PWM rectifier—seven-level NPC VSI. The results obtained show that the input DC voltages of the inverter are not stable but are better than the ones obtained with a cascade which uses one PWM rectifier. To improve the performance of the proposed cascade and stabilize the input DC voltages, the authors propose in this paper a solution which uses a clamping bridge. This study allows a solution to be found 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.