Effect of supercapacitors on the operation of an air-cooled hydrogen fuel cell

Abstract

One of the greatest challenges associated with efficient energy use in unmanned aerial vehicles (drones) is that of the energy storage systems – more specifically it's weight and capacity. Current hydrogen fuel cell drones have very promising flight durations, but have a low power density thus performing poorly at peak power demands. Supercapacitors are known to have high power densities and respond significantly well to peak power demands. For this research it is desired to evaluate how supercapacitors can affect the operation of an existing hydrogen fuel cell system, when combined. This study will include the evaluation of the viability of a DC-DC converter used to reduce the size (and subsequently, weight) of a supercapacitor bank. It also evaluates whether specified switching of the sources has an effect. Using data generated from the experiment it was determined that the DC-DC converter (with efficiency >94%) reduced the efficiency (by 0.5%) and duration (by 3.8%) of the supercapacitor bank whilst increasing the weight (by 16.7%). It was also seen that the method of selective switching offered no benefit over that of a self-selecting system, where the former obtained 223 s of usability and the latter 365 s. However, comparing all the results it was observed that the addition of a supercapacitor bank allowed for an improvement in energy- and power density, of the hydrogen fuel cell system, from 0.65 Wh/kg to 1.19 Wh/kg and from 69.7 W/kg to 125.7 W/kg, respectively.

A Comparative Review of Capacity Measurement in Energy Storage Devices

“…A higher initial SOC can result in a faster capacity fade rate for cycling [6], but this is different for cells under storage. For calendar loss, high SOC either has a significant influence on capacity fading [7] or has no influence at all [8]. High temperature is found to be an additional stress factor for capacity fading [9][10][11].…”

“…The simplest form of an EMT is using the topological arrangement of the ESDs to promote autonomous voltage equalisation across the connections; this is discussed in A. Townsend et al's work [8]. A more complicated EMT can contain an array of electronic switches (transistors, relays) aimed at intelligent control of the ESD or arrangement [9][10][11][12][13][14][15].…”

A Comparative Review of Lead-Acid, Lithium-Ion and Ultra-Capacitor Technologies and Their Degradation Mechanisms

“…From previous experimentation, Townsend et al [232], the order of the connections can have an effect on the usage of the sources. In the case study, experimentation combined two sources to provide a load using a topological EMS.…”

“…This is mainly achieved through the allocation of the HESS [231]. A basic strategy is achieved through topological control (a strategy referring to the placement of the sources with respect to the load [232])-this can include bi-directional or uni-directional flow of current.…”

“…In the case study, experimentation combined two sources to provide a load using a topological EMS. One test placed both sources before the load and another placed the load between the sources [232]. This strategy does not require any electronic control or switching between the sources, is a very basic EMS and provides a benefit of a less complex, smaller sized and lighter system but does not deliver the most optimal HESS [232].…”