A system for controlling a power-converter device of a DC/DC type, having an input connected to a first electric battery at an input voltage, and an output connected to a second electric battery at an output voltage, and being provided with: a transformer stage, with a primary winding coupled to the input, and a secondary winding coupled to the output; a switching stage, arranged between the input and the primary winding and supplying an alternating electrical quantity to the primary winding as a function of the input voltage; a rectifier stage arranged between the secondary winding and the output for generating the output voltage. A control stage switching controls the switching stage at a switching frequency, as a function of a measurement signal indicative of an electrical output quantity, by means of a digital average-current-mode control, obtaining the measurement signal by means of a subsampling of the electrical output quantity, at a sampling frequency, lower than the switching frequency.