Voltage and current ripple considerations for improving ultra-capacitor lifetime while charging with switch mode converters

Ultra-capacitors or supercapacitors that store energy for powering downstream converters used for power conversion need to be charged. When switch mode converters/power supply are used for charging, the significant change in their capacitance with frequency and higher ESR can result in significantly higher voltage ripple in these capacitors. This results in over voltage and temperature rise in these capacitors resulting in their consequent reduction of lifetime. Based on extensive measurements of this charging voltage ripple and charging current ripple at different converter switching frequencies, design considerations that can significantly reduce this voltage and current ripple is proposed in this paper.