Compensation method of AC-to-DC converter characteristics under unbalanced three-phase AC side voltage

The assumption of characteristics analysis of a three-phase AC-to-DC converter is based on a balanced three-phase AC side voltage. When the AC side voltage is unbalanced, the characteristics of the AC-to-DC converter become worse (the AC side currents are distorted and the DC side voltage includes low-order frequency components). Accordingly, a compensation method of the AC-to-DC converter characteristics under unbalanced three-phase AC side voltage, is proposed by authors. The compensation method by feed-forward control is investigated by using a new topology AC-to-DC converter in this paper. In both simulated results and experimental results in a laboratory prototype system having the output power of 10 kW, it is clear that the proposed compensation method maintains the AC-to-DC converter characteristics whereas the three-phase AC side voltage is unbalanced. However, when a value of an unbalanced rate, k', of each effective value to a three-phase average value is lower than a value of modulation factor of a basic sinusoidal reference signal, both the AC side current distortion and the DC side voltage ripple increase due to over-modulation.