Problems and solutions associated with the operation of phase-controlled rectifiers under unbalanced input voltage conditions

The authors analyze the effect of input voltage unbalances on the rectifier input current and on the filter kilovoltampere rating. The effect of voltage unbalance on the rectifier output voltage is examined, and a specific practical solution for the elimination of the triplen input current harmonics is proposed. The authors conclusively demonstrate that the elimination of these noncharacteristic harmonics can be accomplished by using a firing scheme that results in equal and equally spaced thyristor conduction periods, irrespective of the degree of unbalance in input voltages. However, the scheme has a drawback: the amplification of the ripple voltage at the rectifier output. These conclusions are verified experimentally using a 5 kVA setup