Two digital-scalar PWM schemes for generating 3-phase unbalanced voltages

In this work, we present two modulation schemes for generating unbalanced voltages with four-leg inverters. The first modulation is an extended scheme of a digital scalar pulse width modulation previously proposed for controlling three-leg inverters. The second one is based on decomposition of the phase reference signals into their symmetrical components. The schemes are compared theoretically and by simulations. As result, we find a complete equivalence between the two techniques in despite of their different formulations. In this paper, we present the fundamentals of both formulations and also the proof of their equivalence. Simulations and experimental implementation using the techniques for controlling an inverter feeding a four-wire, three-phase load show the effectiveness of both techniques.