A DC link-modulated three-phase converter

This paper proposes a DC link modulation method for three-phase inverters that can reduce losses by suppressing phase-leg switching during two-thirds of the fundamental period. The scheme is advantageous for inverters that operate at a high modulation index, such as PWM rectifiers, active filters or UPSs. The method involves clamping the phase-leg producing maximum voltage to the positive rail and the phase-leg producing minimum voltage to the negative rail, while the third phase-leg is pulse-width modulated. A PWM ripple is added to the DC link to allow the output voltage across the two bus-clamped phases to follow the reference command. In effect, each phase leg is clamped to the positive bus for a third of the fundamental period, clamped to the negative bus for another third and modulated only during the remaining third. This is in contrast to a regular PWM inverter where the phase-legs are continuously switched throughout the fundamental period.