Abstract: This power supply system for powering an element (18), among a rotor (18) and a stator, of an electric machine, includes: a converter (30) for converting a direct input current into a polyphase alternating output current including a plurality M of phases, the converter (30) including two input terminals (42A, 42B), the converter (30) being arranged at the input of the element (18) and being adapted to delivering the polyphase alternating current to the element (18), a controller (32) for controlling the converter (30), a storage bank (34) including at least one storage capacitor (66, 68) arranged between the input terminals (42A, 42B) of the converter, and a device (36) for protecting the element (18) from over-voltages and/or over-currents of said polyphase alternating current, arranged between the converter (30) and the element (18), and including a plurality of switching arms (76) arranged between the respective phases of the polyphase alternating current, each switching arm (76) including two thyristors (