An uninterruptible power supply (120; 200) comprising: a line terminal configured to be coupled to a doubly fed induction generator (DFIG) and an electric grid, the electric grid configured to transmit grid power to said line terminal, the DFIG configured to generate regulated power and including a stator and a rotor; a load terminal configured to be coupled to a load that has a demanded power; a double-conversion circuit configured to be coupled to said line terminal and said load terminal, said double-conversion circuit including an alternating current-to-direct current (AC/DC) converter and a direct current-to-alternating current (DC/AC) converter, said double-conversion circuit further configured to regulate grid power transmission from said line terminal to said load terminal; a bypass circuit configured to be coupled to said line terminal and said load terminal, said bypass circuit further configured to deliver the regulated power to said load terminal when the grid power is unavailable; characterized in a synchronize circuit configured to be coupled to said double-conversion circuit and the DFIG, said synchronize circuit further configured to inject a current from said double-conversion circuit into the DFIG when the grid power is unavailable, the current configured to synchronize the regulated power generated by the DFIG to the demanded power; further comprising a battery coupled to said double-conversion circuit between the AC/DC converter and the DC/AC converter, said battery configured to provide the demanded power to said load terminal when transitioning between the grid power and the regulated power; and when regulated power is synchronized transition from battery to DFIG to provide the demanded power to said load terminal; and wherein, when said battery is configured to provide the demanded power to said load terminal, said battery is also configured to provide cranking power to said DFIG through the DC/AC converter and the bypass circuit to the stator, such that said DFIG is configured to operate as an induction motor and to crank the rotor, whereby the rotor is then connected to the UPS through the synchronise circuit. a line terminal configured to be coupled to a doubly fed induction generator (DFIG) and an electric grid, the electric grid configured to transmit grid power to said line terminal, the DFIG configured to generate regulated power and including a stator and a rotor; a load terminal configured to be coupled to a load that has a demanded power; a double-conversion circuit configured to be coupled to said line terminal and said load terminal, said double-conversion circuit including an alternating current-to-direct current (AC/DC) converter and a direct current-to-alternating current (DC/AC) converter, said double-conversion circuit further configured to regulate grid power transmission from said line terminal to said load terminal; a bypass circuit configured to be coupled to said line terminal and said load terminal, said bypass circuit further configured to deliver the regulated power to said load terminal when the grid power is unavailable; characterized in a synchronize circuit configured to be coupled to said double-conversion circuit and the DFIG, said synchronize circuit further configured to inject a current from said double-conversion circuit into the DFIG when the grid power is unavailable, the current configured to synchronize the regulated power generated by the DFIG to the demanded power; further comprising a battery coupled to said double-conversion circuit between the AC/DC converter and the DC/AC converter, said battery configured to provide the demanded power to said load terminal when transitioning between the grid power and the regulated power; and when regulated power is synchronized transition from battery to DFIG to provide the demanded power to said load terminal; and wherein, when said battery is configured to provide the demanded power to said load terminal, said battery is also configured to provide cranking power to said DFIG through the DC/AC converter and the bypass circuit to the stator, such that said DFIG is configured to operate as an induction motor and to crank the rotor, whereby the rotor is then connected to the UPS through the synchronise circuit.