Analysis and calculation of DC-link current and voltage ripple for three-phase inverter with unbalanced loads

In this paper, the analysis and calculation of the dc-link current and voltage ripple are presented for three-phase inverter with unbalanced load. The average and rms values of the dc-link current are derived. It is found that the rms value is independent of the modulation strategy and switching frequency. Apart from the high frequency harmonics, the current and voltage ripple consists of double fundamental frequency harmonic, which is different from the balanced load. Moreover, the peak-to-peak value of the dc-link ripple voltage caused by the double fundamental harmonic is calculated. Experimental results are shown to verify the accuracy of the theoretical analysis. The analytical and calculated results can be used to guide the dc-link capacitor design.