In this paper, a general powerful circuit of a universal custom power conditioner (UCPC), which is used to improve power reliability and quality applied to distribution networks, is presented in detail. UCPC is based on series and shunt tri-level PWM converters with a battery energy storage system (BESS) for multi-function operations such as harmonic elimination, reactive power control, voltage sags compensation and uninterruptible power supply (UPS). The basic algorithm of system is deadbeat control with repetitive compensation strategy based on voltage space vector PWM method. Some simulation results are use to verify that UCPC can synthetically fulfdl different compensation functions.