Characteristics of AC-Powered DC Motor Controls Using Three and Six Controllable Elements

A great deal of confusion exists as to the waveshapes of the voltage and current presented to the dc load from a 3-and six-controllable-element ac-powered motor control. Of more importance is the question of the effect of these waveshapes on the operation of the dc motor load and on the ac system feeding the motor control. Of particular significance is the effect of the discontinuous current caused by the controlled rectifiers on the measurable power factor of the ac supply feeding the motor control. The intent of this paper is to present a simplified explanation of these effects and their significance.