Energy Storage for Hybrid Military Vehicles

The benefits of hybrid electric vehicles have been recognized by the U.S. Army and other military services. As a consequence, hybrid vehicles are being considered as future combat and tactical platforms. In order to achieve an All Electric Combat Vehicle (AECV), integration challenges have to be overcome for every system in the new vehicle.

Energy storage is one of the major systems of concern in the hybrid electric application. While a number of energy storage devices and concepts have been considered, the focus of this article is on rechargeable battery systems, their suitability, challenges, and limitations. We’ll discuss the integration and application of energy storage in hybrid vehicles, and explore the challenges and various solutions that have been proposed to obtain a functional, reliable, and safe energy storage solution in future AECVs.

Unlike present commercial vehicle designs, the energy storage requirements in military vehicles extend beyond loadleveling of the main voltage bus. In military vehicles, energy storage is required for silent watch and silent mobility applications. These vehicle operations have to be conducted independently of an internal combustion power source. Both high power and high energy capacity are critical for mission implementation and must be delivered from the battery pack. Also required are the related cooling and electronic controls that must be included and must fall within the constraints of very limited space and weight vehicle requirements. In addition, the battery voltage is normally limited to 2-4 volts at the cell level, up to 50 volts at the module level, and 300 volts at the pack level. Thus, in most cases, a bidirectional DC/DC converter is required between the battery and the bus to maintain safe and reliable operation. The photo shows one proposed arrangement for achieving the vehicle energy storage objective. Although less than optimal in terms of energy density with respect to packing efficiency, the use of cylindrical cells provides ready-made channels for air-cooling the battery pack.