Current injection in a controlled rectifier under unbalanced supply and variable line and load inductances

A technique to achieve an efficient and low-cost three-phase controlled rectifier with a power factor of unity is described. This is based on replacing the bulky transformer/inductor commonly used for current injection by lightweight static switches. The proposed technique can be applied as a retrofit to a variety of existing thyristor converters. It consists of a three-phase thyristor bridge, three bi-directional static switches and a current shaping network. The bi-directional switches are switched at only double the line frequency. The current shaping network consists of only two capacitors and three resistors apart from the R-L-C network proposed previously. The scheme also provides a simple, light, fast and economical upgrading to the existing controlled rectifier-based DC drives. This scheme in general is suitable for the common variable medium-to high-power level DC load applications.