Based on the concept of customer power, the paper proposed a new device that is universal custom power conditioner (UCPC). The UCPC has series and shunt power converters with a battery energy storage system (BESS) for multi-function operation to compensate the voltage variation, flicker, reactive power, harmonics, imbalance, unintermptiblc power supply, peak load power supply, active and reactive power control in transmission system. The circuit and control topologies are addressed. A control structure based on dual DSP TMS320C32 and synchronous A/D sampling technology an discussed.