A conversion device for an electric vehicle, enabling electric energy to be transferred between a DC power supply and an N-phase AC power supply, N being an integer higher than or equal to 1, the conversion device including: - a DC-DC converter comprising: - a low voltage branch connected between a first low voltage terminal and a second low voltage terminal, and a high voltage branch connected between a first high voltage terminal and a second high voltage terminal, each of the low voltage branch and the high voltage branch comprising two sub-branches in series connected to each other at a middle point, each sub-branch comprising a switching module; - a first switch connected between the first low voltage terminal and the first high voltage terminal, and a second switch connected between the second low voltage terminal and the second high voltage terminal; - a transformer comprising a primary winding and a secondary winding magnetically coupled to each other, the primary winding being connected, through one of its ends, to the middle point of the low voltage branch, and through the other of its ends to a primary voltage reference, and the secondary winding being connected, through one of its ends, to the middle point of the high voltage branch, and through the other of its ends to a secondary voltage reference; - an AC-DC converter connected on the one hand to the first high voltage terminal and to the second high voltage terminal of the DC-DC converter, including N connection points each able to be connected to a corresponding phase of the AC power supply; - a controller configured to drive the ON or OFF state of the first switch, of the second switch and of each switching module, the controller being further configured to drive the AC-DC converter to transfer electric energy from the DC-DC converter to the AC power supply, or from the AC power supply to the DC-DC converter. - a DC-DC converter comprising: - a low voltage branch connected between a first low voltage terminal and a second low voltage terminal, and a high voltage branch connected between a first high voltage terminal and a second high voltage terminal, each of the low voltage branch and the high voltage branch comprising two sub-branches in series connected to each other at a middle point, each sub-branch comprising a switching module; - a first switch connected between the first low voltage terminal and the first high voltage terminal, and a second switch connected between the second low voltage terminal and the second high voltage terminal; - a transformer comprising a primary winding and a secondary winding magnetically coupled to each other, the primary winding being connected, through one of its ends, to the middle point of the low voltage branch, and through the other of its ends to a primary voltage reference, and the secondary winding being connected, through one of its ends, to the middle point of the high voltage branch, and through the other of its ends to a secondary voltage reference; - a low voltage branch connected between a first low voltage terminal and a second low voltage terminal, and a high voltage branch connected between a first high voltage terminal and a second high voltage terminal, each of the low voltage branch and the high voltage branch comprising two sub-branches in series connected to each other at a middle point, each sub-branch comprising a switching module; - a first switch connected between the first low voltage terminal and the first high voltage terminal, and a second switch connected between the second low voltage terminal and the second high voltage terminal; - a transformer comprising a primary winding and a secondary winding magnetically coupled to each other, the primary winding being connected, through one of its ends, to the middle point of the low voltage branch, and through the other of its ends to a primary voltage reference, and the secondary winding being connected, through one of its ends, to the middle point of the high voltage branch, and through the other of its ends to a secondary voltage reference; - an AC-DC converter connected on the one hand to the first high voltage terminal and to the second high voltage terminal of the DC-DC converter, including N connection points each able to be connected to a corresponding phase of the AC power supply; - a controller configured to drive the ON or OFF state of the first switch, of the second switch and of each switching module, the controller being further configured to drive the AC-DC converter to transfer electric energy from the DC-DC converter to the AC power supply, or from the AC power supply to the DC-DC converter.