A novel design scheme for improving Ultra-Capacitor lifetime while charging with switch mode converters

While it is important that ultra-capacitors should be charged to their maximum rated voltage for getting maximum energy out of them, at the same time any overcharging or temperature rise reduces their lifetime. When charging ultra-capacitors with switch mode converters, the ripple current through them and the significant change in their capacitance with frequency can result in higher voltage ripple, temperature rise and consequent lifetime reduction. Based on extensive practical measurements of the charging voltage ripple and charging ripple current made on an ultra-capacitor bank, a novel design scheme that significantly reduces the charging voltage ripple and charging ripple current resulting in significant improvement of their lifetime performance is proposed in this paper.