Research On Multilevel Inverter

Multilevel voltage source inverter(MVSI), especially for the multilevelneutral-point-clamped voltage source inverter (MNPC VSI), plays a very important rolein the area of high-power high-voltage applications. Due to the significant advantagesoffered by MNPC VSI, such as lower harmonic content，high-quality output waveformsand the possibility of further reducing the required number of the power semiconductorswitches, MNPC VSI has received extensive research.Recently, three-level neutral-point-clamped voltage source inverter(TNPC VSI) isthe most popular among the multilevel converter topologies for high voltage, highpower applications. Having the ability to generate multilevel output voltages, MNPCVSI，for example the five-level neutral-point-clamped voltage source inverter, is able toproduce better quality output waveforms than TNPC VSI in terms of harmonic content,but at the cost of higher number of power semiconductor device requirement and morecomplicated modulation strategy.In this research work a novel five-level voltage source inverter and a newthree-level voltage source inverter are proposed. The first proposed converter is a hybridcombination between a five-level buck stage and a two-level voltage source inverter.This multilevel inverter has a simpler circuit configuration and is able to generatefive-level output voltages. The second proposed converter is also hybrid combinationbetween a ‘alterable voltage source’ and a two-level voltage source inverter. Thismultilevel inverter also has a simpler circuit configuration and is able to generatethree-level output voltages. What’s more, it has no the neutral-point balancing problem.Compared to the traditional three-level neutral-point-clamped voltage source inverter,this inverter can improve the quality of the output waveforms.In this work a comprehensive space vector simulation study is carried out toinvestigate the operation of the proposed inverters. Finally, the output performance ofthe proposed inverters is compared to the conventional voltage source inverters in orderto identify the advantages and disadvantages of the proposed voltage source inverters.