Power Electronics Handbook

216 Direct a.c. frequency converters

transformer has also been appreciably reduced. Furthermore, it is now

difficult to maintain a balanced supply to the three-phase load. In spite of

this,

the system is often economical to use in low-power circuits, where

good performance is not a prime criterion. Figure 10.12 shows an

alternative form of asymmetrical six-pulse converter, which consists of a

ring arrangement of bi-directional a.c. to d.c. converters and is therefore

not made from basic single-phase cycloconverter modules. As is seen, the

component content has been reduced by 50% over comparable

Converter

I

T^-THu.

3 phase

a.c. supply

fîîlî ...