In the paper the research results of digital single-loop control system for supercapacitor energy storage as an element of hybrid power supply of frequency-controlled alternating current electrical drive are presented. The integration of a supercapacitor energy storage device into the electric drive is made by using the bidirectional DC-to-DC converter. The description of laboratory testbench setup, structure and mathematical model of digital single-loop automatic control system are given. Mathematical simulation and experimental evaluation of the digital control system performance have been carried out.