Three-phase circuits with voltage control by integral-cycle single-phase mode triggering of thyristors

Abstract

Several configurations of balanced three-phase series RL loads are investigated to consider the feasibility of using thyristor control with integral-cycle triggering. The four-wire star-connected load, with pairs of thyristors in the supply lines and the deltaconnection with pairs of thyristors in the load legs, are found to be suitable. Both connections result in similar load voltage and current waveforms. The branch-delta connection is considered to be preferable because the supply lines do not contain dc components of current.0093-9994/82/0900-0507S00.75 © 1982 IEEE

Harmonics Phase Shifter for a Three-Phase System with Voltage Control by Integral-Cycle Triggering Mode of Thyristors

“…The resulting threeload voltage waveforms are identical and so are the three-load current waveforms. The supply frequency components are found to be balanced, since they are 120 o apart in time-phase while the phase displacement angles of a particular subharmonic or higher order harmonic are unbalanced [11,12] . Due to the unbalanced phase relationships of the subharmonic components, these components represent a source of trouble when these voltage waveforms are used to feed ac machines for speed control purposes [11] .…”

“…This is because the amplitudes and phase displacement angles of the higher order harmonic and subharmonic components of the integralcycle controlled waveform are determined by the conduction period N and the control period T and the order of the individual harmonic. The three-phase analysis of voltage and current waveforms and phase relationships of the generated harmonic and subharmonic components for different circuit configurations are described in [12,13] .…”

“…Let the notation 1, 2, 3 denote the three phases A, B and C respectively. Thus the load voltage (v Lj ) for any j th phase will have the general form [12] .…”