Stabilization of multi DC bus link voltages of multilevel NPC VSI. Application to double stator induction motors

Voltage source multilevel inverters have become very attractive for power industries in power electronics applications during last years. The main purposes of studying multilevel inverters are the generation of output voltage signals with low harmonic distortion and reduction of switching frequency. An important issue of the multilevel inverter is the capacitor voltage-balancing problem. The unbalance of different DC voltage sources of multilevel neutral point clamped (NPC) voltage source inverter (VSI) constitutes the major limitation for the use of this new power converter. In this paper, we present study on the stability problem of the input DC voltages of the three-level Neutral Point Clamping (NPC) voltage source inverter (VSI). This inverter is useful for application in high voltage and high power area. In the first part, we remind the model of double stator induction motors (DSIM). Then, we develop control models of this inverter using the connection functions of the semi-conductors. We propose a Pulse Width Modulation (PWM) strategy to control this converter. The inverter is fed by constant input DC voltages. In the last part, we study the stability problem of the input DC voltages of the inverter. A cascade constituted by two three-level PWM rectifiers - two three-level NPC VSI - DSIM is discussed. The results obtained show that the input DC voltages of the inverters are not stable. To solve this problem, we propose to use a half clamping bridge. This solution is very promising in order to stabilize the input DC voltages of this converters.