An uninterruptable power supply (UPS) system for providing power to a load coupled to a utility power source is provided. The UPS system includes a doubly-fed induction generator (DFIG), a rechargeable energy storage system, a first inverter, and a controller in communication with the DFIG and the first inverter. The DFIG includes a stator and a rotor coupled to the load. The stator and rotor are magnetically coupled together. The DFIG generates an auxiliary power output. The first inverter is coupled between the rotor and the rechargeable energy storage system. The controller detects a power disturbance associated with the utility power source and controls the first inverter to provide an excitation input to the rotor in response to the power disturbance. The DFIG provides the auxiliary power output to the load based on the excitation input.