The paper clearly identifies the inverter voltage-distortion mechanisms that are present in large VSI drives due to inverter delay and turn-off times as well as snubber circuit operation. A fast-frequency domain model for computing the DC-input harmonics of such a drive is also presented. The paper shows that this model may be extended to include the distortion mechanisms discussed. The accuracy of the model is confirmed by comparing the computed and measured input-current harmonics for a range of inverter delay times commonly used in traction VSI drives.