The research considers the problem of maintaining the voltage on the DC bus of a frequency converter with an autonomous inverter, which is part of an alternating current electric drive with a frequency method of speed control. The electric drive is equipped with an energy storage device with integrated supercapacitors coupled to a DC bus through a reversible step-down DC-DC converter. In the research, an approach for maintaining the DC bus voltage at a preset level by compensating the load current of an autonomous inverter with an external current of the energy storage is proposed, that solves the main issue. Energy accumulator is equipped with single-circuit servo current control system. The study considers several variants of current control systems based on the principle of combined control. The goal of this research is to evaluate the accuracy of voltage stabilization on the DC bus of an autonomous inverter. Also presented theoretical analysis of current control systems error coefficients. The simulations of the electric drive are carried out with and without accounting the discreteness of the energy storage converter. The results of the study can be useful in the development of systems for optimizing energy storage with supercapacitors for various applications.