Choosing the right converter system for electric tractive units equipped with threephase traction motors

Due to the progress made in the field of thyristor converters, three-phase squirrel-cage induction motors have gained considerably in importance as traction motors for electric or diesel-electric railways. Two converter systems are now available for use in railway tractive units; (1) the voltage link converter using a pwm inverter as a machined-side unit; (2) the current link converter using a phase-sequence commutated inverter. A brief description of the modes of operation of the two inverter types is followed by a comparative evaluation of the technical characteristics important for railway applications and of the complexity and cost of the two converters. Both inverters are found to function satisfactorily, but the phase-sequence inverter has an advantage because it is less complex, more reliable and easier to protect. For the covering abstract of the conference see IRRD no 288720. (TRRL)