Comparative Study of Constant Switching Frequency and Variable Switching Frequency Multicarrier Pulse width Modulation for Three Phase Cascaded Multilevel Inverter

This Paper Presents a comparative study of Constant Switching frequency Multicarrier Pulse width Modulation and Variable Switching frequency Multicarrier Pulse width Modulation. The emergence of Multilevel converter has been in increase since the last decade . These new type of converters are suitable in high voltage & high power application due to their ability to synthesize waveforms with better harmonic spectrum. In this paper two novel methodologies Multicarrier subharmonic Pulse width modulation and Multicarrier switching frequency optimal pulse width modulation using constant switching and Variable switching frequency is compared. The Multicarrier subharmonic pulse width modulation Cascaded Multilevel Inverter strategy reduced output Total harmonic distortion and Multicarrier switching frequency optimal pulse width modulation Cascaded Multilevel Inverter strategy enhances the output Voltages. 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, 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.