Analysis and design of forced commutation circuit for by-pass thyristor-based AC-DC converters

In by-pass thyristor based AC-DC bridge converters, the by-pass thyristor can be either a conventional thyristor or a GTO thyristor. Generally, when the turn off facility is added to the by-pass thyristors, the total harmonic distortion (THD) of the supply current is reduced and the input power factor is successfully improved. This paper presents an alternative modified scheme, where forced commutation is applied to the conventional by-pass thyristors instead of using GTO thyristors. The complete analysis and design of a forced commutation circuit is presented for the single-phase bridge converter with conventional by-pass thyristors. Analytical and experimental results illustrating the benefits obtained from applying forced commutation are presented and discussed.