This paper extends a matrix method to analyse a three phase dual converter-DC motor drive in circulating-current modewhen both the thyristor bridges are conducting simultaneously. The AC side source impedances have been taken into account in the analysis. A simplified but efficient digital computer program is developed to deal with the periodically varying topology of the system and it is able to automatically assemble the dynamic equations of the system for any mode of operation with the help of a system state array containing the conduc-tion states of the thyristors. The validity of simulation program is tested by comparison of the typical computed results with the analytical results obtained by another approach elsewhere.