Purpose: To substantiate the circuit design and algorithms for individual smooth and automatic control of single-phase direct current electric locomotives according to the laws of constant traction force and constant power without breaking the electric locomotive power circuits in order to increase the efficiency of its electric drive with controllable traction motor excitation converters. As a circuit design solution, it is proposed to apply a power electrical circuit with two rectifier-inverter converters for each section of the electric locomotive for bogie-based traction control, as well as individually controlled bridge transistor converters, shunting field windings, for axial traction control within each bogie. Methods: The development of circuit solutions using modern power semiconductor converters; theory of automatic control and design of finite state machines; mathematical modeling of electromagnetic, electromechanical and mechanical processes. Results: The developed control algorithms provide the possibility of obtaining traction characteristics of an electric locomotive that vary according to the laws of constancy of traction force or constancy of power, bringing the traction characteristics of electric locomotives with collector traction motors to the characteristics of electric locomotives with asynchronous traction motors. The calculations performed confirmed the possibility of implementing an algorithm for individual control of traction motor currents and their excitation currents, as well as traction forces, which ensures a smooth increase in the traction force of an electric locomotive.Practical significance: The developed technical solutions applicable in the manufacture of modern and modernization of operated electric locomotives will ensure an increase in the traction properties of singlephase DC electric locomotives and will contribute to an increase in the throughput and carrying capacity of the railway network.