Design of Battery-Super Capacitors Combination in Uninterruptible Power Supply (UPS)

This paper presents a study of the reduction in battery stresses by using Super capacitors (SCs) in UPS. We aim at investigating the optimal Super capacitors-battery combination versus the SCs cost. This investigation is threefold; first, super capacitors and battery models developed using MATLAB/ Simulink are presented and validated. Second, the architecture and the simulation of the designed system that combines the SCs and the battery are shown. The Super capacitors are used as high-power storage devices to smooth the peak power applied to the battery during backup time and to deliver full power during short grid outages. By charging the SCs through the battery at a suitable rate, all impulse power demands would be satisfied by the Super capacitors. Third, extensive simulations are carried out to determine the gain in battery RMS current, the gain in energy losses, the energy efficiency and the elimination rate of surge load power. These four performance parameters are determined by simulation and then analyzed.