Multigroup convertors with series a.c. connection

The paper presents an analysis and assessment of multigroup convertors with the group transformers connected in series on the a.c. side. Two such arrangements are examined; one with series connection and the other with parallel connection of the d.c. side. The d.c. and a.c. characteristics are derived for rectification and inversion, and it is shown that, if these two types of convertor are supplied by the same a.c. system, the lowest-order harmonic on the a.c. side is the 23rd. This is achieved with ordinary delta-star, star-star transformers. The suggested arrangement operates at a considerably higher power factor, but it is inferior with regard to the rating of rectifying elements and transformers when compared with the conventional multigroup convertor.