This paper presents the comparison of various Pulse Width Modulation (PWM) strategies for the three phase Diode Clamped Multi Level Inverter (DCMLI). The main contribution of this paper is the proposal of new modulation schemes with Variable Amplitude (VA) and various new schemes adopting the constant switching frequency and also variable switching frequency multicarrier control freedom degree combination concepts are developed and simulated for the chosen three phase DCMLI. The three phase DCMLI, is controlled in this paper with Sinusoidal PWM (SPWM) reference along with triangular carriers and analysis is made among both without carrier overlapping and with Carrier Overlapping (CO) techniques to choose the better strategy by performing simulation using MATLAB-SIMULINK. The variation of Total Harmonic Distortion (THD) and fundamental RMS output voltage is observed for various modulation indices. It is observed that among the various equal amplitude PWM strategies, COPWM-C provides less THD and higher RMS voltage. It is recognized that among the various variable amplitude PWM strategies, VACOPWM-C provides less THD and VACOPWM-B provides higher RMS voltage. By comparing the equal amplitude PWM strategies with the variable amplitude PWM strategies it is inferred that VACOPWM-C provides less THD and VACOPWM-B provides higher RMS voltage. It is also inferred that carrier overlapping techniques provides better results compared to the without carrier overlapping techniques.

This paper presents the comparison of Unipolar Inverted Sine Carrier Pulse Width Modulation (UISCPWM) techniques for the Cascaded Multi Level Inverter (CMLI). Due to switch combination redundancies, there are certain degrees of freedom to generate the multilevel AC output voltage. This paper presents the use of Control Freedom Degree (CFD) combination. The effectiveness of the pulse width modulation strategies developed using CFD are demonstrated using simulation. The results indicate that the chosen five level inverter triggered by the developed UISC phase shift PWM and UISC variable frequency PWM strategy with sine and stepped wave references and UISC alternate phase opposition disposition PWM strategy with 60 degree reference exhibit reduced harmonics and UISC carrier overlapping PWM provides higher fundamental RMS output voltage for all three chosen references. Simulations are performed using MATLAB-SIMULINK.