First Harmonic Ripple Compensation for Active Split DC-Link 4-Wire Inverters

This paper proposes a multi-carrier modulation in which the carriers’ phase-shifts of a four-leg three-phase inverter with active split dc-link are dynamically displaced to cancel the first harmonic of the current flowing into the active split dc-link capacitors. The advantages of removing the first harmonic of the ripple, namely, the most energetic one, allow advantages including better efficiency and reduced capacitor volume. The proposed modulation aims at carrier phase-shifts tuned to reach harmonic cancellation over a whole grid cycle. To this end, it is shown that two phases can freely rotate while the remaining phases should be appropriately phase-shifted with respect to the other two. This allows the reduction of circulating rms currents or other specific harmonics undesired in specific applications. The proposed modulation is validated on an experimental prototype, proving the first harmonic cancellation effect.