Improvement of Input and Output Performance for Three-Level Three-Phase UPS System Using Fast Transient Repetitive Controllers

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 (T_p) for the rectifier and one sixth of T_p 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.