Ripple Reduction of Active Split DC-Link 4-Wire Inverters by Phase-Shifted Multi-Carrier Modulation

This paper considers a multi-carrier modulation in which the phase-shifts between the carriers are adjusted to reduce the rms current flowing into the active split dc-link capacitors of four-wire three-phase inverters when the neutral node is modulated with the third harmonic. Capacitors current reduction is beneficial in terms of volume, losses, and components stresses. Considering the current ripple combination of the phases and neutral currents, the proposed approach reduces the rms current through the split dc-link capacitors compared to a standard single-carrier pulse-width modulation. It is shown that the amount of reduction depends on the modulation index and the ratio between the neutral and the output inductors. Besides, it is not significantly influenced by the unbalancing current, in the considered topology, in which the split dc-link capacitors are aimed to regulate the neutral-point voltage. Guidelines for selecting suitable phase-shifts in practical cases based on the inverter operating point are discussed. The results are demonstrated on an experimental prototype.