EXPERIMENTAL INVESTIGATION OF THREE LEVEL PWM CONVERTER

Abstract

The multilevel power converter was first introduced nearly twenty years ago. The basic concept involved is utilizing a higher nuTnber of semiconductor switches to perform the power conversion in small voltage steps. There are advantages of this approach when compared with traditional (two level) power conversion, some of which are production of higher power quality waveforms, reduction in dv/dt stresses on the load and lesser electromagnetic interference. Also lower voltage semiconductor switches can be used in multilevel converters. One clear disadvantage of the multilevel converters is the higher number semiconductor switches and each switch has its own gate circuitry which further increases the complexity of circuit. Another disadvantage of the multilevel converters is that different voltage levels can be achieved either from isolated voltage sources or from a bank of series capacitors. But isolated voltage sources are not always available, so we have to depend on capacitor bank with which problem of dc voltage imbalance is associated. However there are certain ways to tackle this problem but that result in complexity and hence the losses in the circuit. Some of the applications of the multilevel converters is in industrial drives, flexible ac transmission systems (FACTS), battery charging and vehicle propulsion etc.