Battery/Supercapacitors Combination in Uninterruptible Power Supply (UPS)

Abstract

This work presents a study of the reduction in battery stresses by using supercapacitors (SC's) in a 500 kVA rated UPS. We aim at investigating the optimal supercapacitors-battery combination versus the SC's cost. This investigation is threefold; first, supercapacitors and battery models developed using Matlab/Simulink® are presented and validated. Second, the architecture and the simulation of the designed system that combines the SC's and the battery are shown. The supercapacitors 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 SC's through the battery at a suitable rate, all impulse power demands would be satisfied by the supercapacitors. 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. The influence of the SC's recharge on the performance indicators is highlighted. A thorough analysis involving optimal study proposes to draw the optimal SC's number and filter constant from the variation of the aforementioned parameters versus the cost of the SC's.

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