The paper presents a device developed on the basis of the adjustable passive reactive power compensator and intended for the increase in the power factor of the electric AC locomotive. Such configuration contributes to the increase in the power factor of a locomotive in its all working modes of operation due to approximation of its power factor value to the maximum possible values. The compensator is operated by the method of extreme voltage control of autonomous voltage inverter. Mathematical modeling of work of an electric locomotive equipped with such compensator was performed with MATLAB package and showed a possibility of increase in the power factor up to 0.98. (C) 2016 Published by Elsevier Ltd.