Optimal Supercapacitor Size to Enhance Battery Life Under Large Intermittent Load Variations

This paper presents the improvement of battery performance by combining a Supercapacitor (SC) and control circuits to extend the battery's life for a standalone residential electricity system. Residential loads such as fridge, air condition, microwave oven, charging systems work intermittently causing pulse load profiles. Rapid and deep discharges often applied to a battery will shorten its lifetime. The proposed system has demonstrated the use of optimum SC size to reduce the height of load pulses and lowering the Depth of Discharge (DoD) on the battery. A bidirectional buck-boost converter is employed to operate the SC in a semi active mode. When the load pulses present, the SC absorbs it through the converter. On other conditions, the converter releases the SC energy to supply the load, which reduces the use of the battery. The research results show that by optimizing the appropriate SC size, the DoD can be reduced significantly, thereby extending the battery lifetime. The data obtained if the battery cycles originally 1950 have been added to SC by 3% of the battery-SC capacity, then the cycles has increased to 2554 or has extended the battery lifetime from 5.34 to 7 years.