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The dc chopper drive of traction motors using thyristors has many advantages such as the improvement of efficiency, stepless control of motor current, and the elimination of mechanical contactors and the associated maintenance. A considerable amount of literature has been published concerning chopper circuitry and its application to dc motor control. There are some problems to be solved, however, for the actual application in electric railways ; the first is the realization of a high-voltage chopper, the second is the reduction of inductive interference, and the third is the reduction of weight and cost of chopper equipment. The characteristics of a multiple phase chopper circuit which has been developed for traction motor control systems are described. The multiple phase chopper with common load has proved to have the excellent property of reducing the higher harmonic components both in input current and in output current. This results in reducing the inductive interference and minimizing the weight of the smoothing reactor.