Analysis of Experimental Investigation of Various Carrier-based Modulation Schemes for Three Level Neutral Point Clamped Inverter-fed Induction Motor Drive

The harmonic analysis of the stepped waveform of the three-level inverter, based on number of triangular carriers and a sinusoidal modulating signal has been described. Analytical solutions of different multilevel pulse width modulation (PWM) strategies for three-level neutral point clamped (NPC) has been presented. Analysis of the total harmonic distortion (THD) of voltage and stator current has been carried out by simulation study. These solutions show that in-phase sinusoidal pulse width modulation (IPSPWM) strategy shows better spectral performance compared to the phase opposite sinusoidal pulse width modulation (POSPWM) and dipolar modulation techniques. This is because of the fact that it places significant harmonic energy in to main carrier component and relies on the cancellation of this component between phase legs when the line-to-line voltages are formed. All these techniques are applied to an induction motor drive for comparison. Torque ripple is also estimated for different techniques. A laboratory model is developed to verify validity of different modulation schemes.