This paper presents an advanced control scheme using enhanced repetitive controller (RC) to improve performance of double conversion three-phase UPS system, which is composed of a three-level Vienna rectifier and a three-level T-type inverter. To guarantee a high-quality output voltage of the UPS, i.e., balanced, and sinusoidal voltage, under various types of loads, a proportional integral (PI) plus RC is employed in the inverter control scheme. Meanwhile, to achieve unity power factor and robust operation for the front-end rectifier of the UPS under adverse grid voltage conditions, an enhanced current controller is developed with a proportional plus RC controller. Compared to previous rectifier’s control methods, the proposed solution is greatly simplified since no phase-locked loop or coordinate transformation is needed. In addition, the proposed RCs have shorter delay compared to previous RC controllers, i.e., one fourth of the fundamental period (Tp) for the rectifier and one sixth of Tp for the inverter. Hence, the dynamic response of UPS system is improved without degrading the steady-state control performance. Various experimental tests of 20-kVA UPS are provided to verify the feasibility of the proposed control system.