Modelling and Control of a Cascade for the Multi DC Bus Supply of a Multilevel NPC Voltage Source Inverter

摘要

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. In this paper, the stability problem of the input DC voltages in a nine-level Neutral Point Clamping (NPC) Voltage Source Inverter (VSI) is recalled and illustrated. A knowledge model of this converter using switching functions and a PWM strategy is detailed. To analysis the instability problem of the input DC voltages of the inverter, we study a cascade constituted by three phase's nine-level PWM rectifier-filter-nine-level NPC voltage source inverter-PMSM. To solve this problem the power structure is modified by adding half clamping bridges across capacitors in order to limit their deviations. Additional control functions are then introduced. The obtained results are full of promise to be used to stabilise the input DC voltages of these converters.