A new duty cycle based efficiency estimation method for a supercapacitor stack under constant power operation

Nowadays, energy storage devices such as supercapacitors or ultracapacitors are available to address the high specific energy (compared to electrolytic capacitors) and high specific power (compared to batteries) applications, and most of them would consist of constant power operation which means that the current handled by the device needs to compensate the variation of the voltage. Also, for most of these applications, a minimum round trip efficiency has to be achieved from the design stage in conjunction with the variation of the voltage and current during a charge-discharge cycle, which would make the estimation of efficiency quite challenging. Based on an analytical model of the supercapacitor power losses, this paper proposes a new methodology to determine the roundtrip efficiency of a supercapacitor stack operating under constant power mode by performing a simple measurement of the charging dutycycle.