Evaluation of an actively contolled battery-capacitor hybrid energy storage module (HESM) for use in driving pulsed power applications

As the U.S. Navy moves towards the fielding of all electric ships (AES), there will be a unique shift in the electrical load profile seen by its generation sources [1,2]. In addition to the electrical propulsion system, unique high pulsed power loads, which have high peak to average power requirements, will be deployed. Traditionally, fossil fuel generators have been used to power ships, but the transient power demands induced by pulsed power loads can impart extreme stress on generators, resulting in a loss in both fuel efficiency and power quality. One solution to this problem involves buffering the generator´s power demand with an energy storage device (ESD). Normally the go-to solution for implementing an ESD might be to utilize lead acid batteries however with recent developments in lithium-ion batteries (LIB), it is desirable to use them instead due to their high combined power and energy density [3-6]. In order to further preserve the lifetime of the LIBs and maintain their safe operation, many have proposed to augment them with electric double layer capacitors (EDLCs). Such a configuration is known as a hybrid energy storage module (HESM) since it incorporates both energy dense LIBs and power dense EDLCs into a single power supply topology [7-9]. A HESM is used to augment the generator in providing power to pulsed loads when they are energized while also acting as a sink to the generator when the pulsed loads are in an idle state. This enables the generator to maintain a nearly constant output, increasing its efficiency and power quality considerably. A few different HESM topologies have been previously presented [8-9]. In the work presented here, an actively controlled LIB as well as an actively controlled EDLC are deployed. This unique configuration is aimed at maximizing the energy density of the LIB while also maximizing the power and energy density of the EDLC. The HESM has been designed, constructed, and validated using only commercial off-the-shelf (COTS) technologies. This paper will present the advantages and capabilities that this type of HESM topology brings to a pulsed power system along with insights into the current abilities of COTS products to facilitate this application.