Carrier-based PWM scheme for three-phase four-leg inverters

This paper presents a pulse-width modulation (PWM) technique for controlling three-phase, four wire voltage source inverters (VSI). It is an extended scheme of a digital scalar pulse width modulation previously proposed for controlling three-leg inverters. The technique is suitable for generating unbalanced voltages and its implementation is simpler than those based on three-dimensional space-vector methods. The performance of the technique is evaluated with regard to the harmonic distortion. This feature is studied both as functions of the free-wheeling distribution ratio and the modulation index. Experimental and simulated results show the effectiveness of the method.