A system for harvesting energy including: an electrical machine including a first and a second structure, movable with respect to each other; a counterweight coupled to the second structure; a power transfer structure, electrically connected between the first structure and the load; an angular position sensor which provides a position signal ({right arrow over (ε)}(t)) indicating the angular position of the counterweight; and an accelerometer which provides an acceleration signal ({right arrow over (a)}(t)) indicating an acceleration which affects the first structure. The system for harvesting energy further comprising a control unit, which includes: a first stage which generates a limit position signal ({right arrow over (ε)}lim(t)) indicating an angular instability region (R-I); and a second stage which controls the power transfer structure based on the position signal and on the limit position signal, so as to modulate the transfer of electrical power to the load so as to prevent the counterweight from entering into the angular instability region.