Investigations on Third Harmonic Injected Control Strategies of Multilevel Inverters for Improved Power Quality

Multilevel Inverter has gained popularity in high power and voltage applications such as electrical power transmission and grid integration of renewable energy source. Multilevel inverter is designed to achieve higher voltage level with low harmonics and without requiring higher ratings of individual devices. In this paper, three modulation strategies based on a Multicarrier level shifted PWM and third harmonic Injected reference has been implemented; the aim of this paper is to compare these three strategies to know their effect on the output voltage quality of the inverter. The three modulation strategies are: Third Harmonic Injected reference In Phase Disposition (THI-IPD), Third Harmonic Injected reference Alternative Phase Opposition Disposition (THI-APOD) and Third Harmonic Injected reference Phase Opposition Disposition (THI-POD). These three strategies are applied to 9-levels diode clamped Multilevel inverter under different operation conditions and different Modulation schemes. The study has been implemented via simulation using MATLAB/Simulink.