Linear Feedback Control of Multi DC Bus Link Voltages of Multilevel NPC VSI Cascade

Voltage source multilevel inverters have become very attractive for power industries in power electronics applications during last years. The main purposes that have led to the development of the studies about multilevel inverters are the generation of output voltage signals with low harmonic distortion; the reduction of switching frequency. A serious constraint in a multilevel inverter is the capacitor voltage-balancing problem. The stability problem of the input DC voltages in a Three-Level Neutral Point Clamping (NPC) Voltage Source Inverter (VSI) is recalled and illustrated in this paper. Power structure is proposed. It consists in using one CV rectifiers but the instability of intermediary DC voltages is observed. To solve this problem the power structure is modified by adding clamping bridges across capacitors in order to limit their deviations. The obtained results are full of promise to be used to stabilise the input DC voltages of this converter.