Multicarrier pulse width modulation methods based three phase cascaded multilevel inverter including over modulation and low modulation indices

Abstract

The multilevel inverter utilization have been increased since the last decade. These new type of inverters are suitable in various high voltage & high power application due to their ability to synthesize waveforms with better harmonic spectrum and faithful output. This paper presents, two proposed scheme adopting the multicarrier pulse width modulation concept. The multicarrier pulse width modulation cascaded multilevel inverter strategy enhances the fundamental output voltage and reduced total harmonic distortion. The multilevel inverter circuit analysis and selection of proper references discussed based on the formulation switching patterns. A three phase five level cascaded inverter is used to explain the methods. The methods can be easily extended to a n-level inverter. The cascaded inverter is subjected to a new modulation scheme, which uses multiple modulating signals with a single carrier. From the modulation scheme, mathematical equations that define the pulse width modulation switching instants are derived. In order to justify the merits of the proposed modulation scheme, harmonic analysis for and measured total harmonic distortion and output voltages are compared and discussed. The method can be confirmed by experimental results obtained using a three phase cascaded five level inverter.