A turbine generator system, comprising: a doubly-fed alternating-current generator having a first poly-phase circuit and a second poly-phase circuit; a poly-phase AC-to-AC converter circuit coupled between the first poly-phase circuit and the second poly-phase circuit and configured to produce a substantially fixed frequency voltage output; characterized in that the turbine generator system further comprises: a poly-phase transformer having input windings coupled to the first poly-phase circuit and having output windings, wherein the poly-phase transformer is configured to increase a voltage of the substantially fixed-frequency voltage output from the AC-to-AC converter circuit for rectification; a uni-directional rectifier circuit coupled to the output windings of the poly-phase transformer and configured to convert poly-phase AC from the transformer output windings to direct current, and a backup power source coupled to the doubly-fed AC generator and configured to power, during startup, the turbine generator system; and wherein the backup power source comprises a battery (910; 1120) coupled to the doubly-fed AC generator via a battery inverter circuit (920, 1110); wherein the backup power source further comprises a flywheel mechanically coupled to the doubly-fed AC generator; and wherein the battery is arranged to power the flywheel. a doubly-fed alternating-current generator having a first poly-phase circuit and a second poly-phase circuit; a poly-phase AC-to-AC converter circuit coupled between the first poly-phase circuit and the second poly-phase circuit and configured to produce a substantially fixed frequency voltage output; characterized in that the turbine generator system further comprises: a poly-phase transformer having input windings coupled to the first poly-phase circuit and having output windings, wherein the poly-phase transformer is configured to increase a voltage of the substantially fixed-frequency voltage output from the AC-to-AC converter circuit for rectification; a uni-directional rectifier circuit coupled to the output windings of the poly-phase transformer and configured to convert poly-phase AC from the transformer output windings to direct current, and a backup power source coupled to the doubly-fed AC generator and configured to power, during startup, the turbine generator system; and wherein the backup power source comprises a battery (910; 1120) coupled to the doubly-fed AC generator via a battery inverter circuit (920, 1110); wherein the backup power source further comprises a flywheel mechanically coupled to the doubly-fed AC generator; and wherein the battery is arranged to power the flywheel. a poly-phase transformer having input windings coupled to the first poly-phase circuit and having output windings, wherein the poly-phase transformer is configured to increase a voltage of the substantially fixed-frequency voltage output from the AC-to-AC converter circuit for rectification; a uni-directional rectifier circuit coupled to the output windings of the poly-phase transformer and configured to convert poly-phase AC from the transformer output windings to direct current, and a backup power source coupled to the doubly-fed AC generator and configured to power, during startup, the turbine generator system; and wherein the backup power source comprises a battery (910; 1120) coupled to the doubly-fed AC generator via a battery inverter circuit (920, 1110); wherein the backup power source further comprises a flywheel mechanically coupled to the doubly-fed AC generator; and wherein the battery is arranged to power the flywheel. wherein the backup power source comprises a battery (910; 1120) coupled to the doubly-fed AC generator via a battery inverter circuit (920, 1110); wherein the backup power source further comprises a flywheel mechanically coupled to the doubly-fed AC generator; and wherein the battery is arranged to power the flywheel.