Fundamental Operation of Rectifiers with Thyristor AC Power Control

The dc output of low-voltage diode rectifiers can be adjusted economically and efficiently by thyristor ac power controllers on the ac side of the rectifier transformer. This method of obtaining voltage control has been used for a number of years. This paper presents an analysis of the various modes of operation, the waveforms, control characteristics, and various other parameters and observations of interest for some commonly employed circuits. In particular the sixpulse bridge rectifier with delta-wye transformer (ASA-23) and the six-pulse double-wye interphase rectifier with delta-double wye transformer (ASA-45) have been studied theoretically as well as experimentally. Attention has been given to the problem of transformer saturation, and the associated requirements for gating accuracy was found to be less stringent than one would expect. It was further discovered that these circuits have some pronounced advantages over the corresponding six-pulse phase controlled converters when comparing dc ripple and reactive power consumption from the line.