A UNIFIED APPROACH IN DETERMINING MODES OF CURRENT CONDUCTION IN FULLY PHASE-CONTROLLED AC TO DC CONVERTERS

Abstract

This paper presents a unified analysis method in the determination of the different modes or aspects of current conduction in fully phase-controlled converters. In this method, continuous load current mode is initially assumed and the unified expressions for the instantaneous load currents for converters with output pulse number greater than one are determined at points of the converter output voltage discontinuities and/or at points of minimum output current values. Modified expression for the instantaneous current value for the converter with one output pulse number is derived. From the signs of these instantaneous current values, the converter output current modes are identified. In the analysis, the control delay angle range is limited to a radians (which is the half cycle angular distance of the ac source voltage) while the duration of the semi-conductor switch turn on signal is maintained constant throughout the control delay angle range. The reported method has the advantage of giving more information than other reported methods available in the literature about the nature/shape of a given converter output current waveform and the degree of load current continuity or discontinuity from the transition of continuous to discontinuous current conduction modes.