A study of supercapacitor charge redistribution for applications in environmentally powered wireless sensor nodes

As an important energy storage device for wireless sensor nodes with energy harvesting capabilities, the characteristics of supercapacitors need to be taken into account in developing power management solutions. While supercapacitor self-discharge is usually considered because it causes voltage decay and energy loss, supercapacitor charge redistribution has not been well examined although this process may result in a greater voltage change than self-discharge. This paper studies the supercapacitor voltage change during charge redistribution. The supercapacitor voltage may increase, decrease, or remain almost constant during charge redistribution depending on the initial state. Three approaches are employed to investigate the supercapacitor voltage change during charge redistribution: analytical estimations, numerical simulations, and experimental measurements. Both the supercapacitor voltage change after a charge process and that after a discharge process are examined. Various parameters of the charge or discharge process such as charge current and discharge time that affect the initial state of supercapacitor charge redistribution are swept. The results obtained using different approaches are consistent. These results can be utilized by wireless sensor network application designers to estimate the supercapacitor voltage change during charge redistribution. (C) 2014 Elsevier B.V. All rights reserved.