Weapon and Armor System Power in Future Combat Vehicles

Wednesday, April 01 2009

Future combat vehicles will require unconventional weapons and armor systems such as electromagnetic (EM) or electrothermal chemical (ETC) guns, electromagnetic (EM) armor, and directed- energy weapons (DEWs). To meet these requirements, a hybrid electric power system has been identified as the best alternative to support the demand for propulsion, continuous auxiliary power demand, and pulsed power demand for weapons and armor.

Although the development of these weapons and armor technologies is progressing at a fast rate and can be demonstrated at a smaller scale today, the power supply needed in the vehicles to support these systems presents a great challenge to technology developers and vehicle integrators.

In a 20-ton combat hybrid vehicle platform, power supply will mainly consist of two sources of energy: a prime power source driving an AC generator such as a heat engine, and an energy storage system consisting of advanced batteries, ultra capacitors, and flywheels, or a combination of these three devices. Currently and in the near term, the prime power will be either a diesel engine or a turbine, and in the far term, fuel cells may become viable options.

The power supply has to meet the demands of mobility, lethality, and survivability. The demand for electric power becomes even more challenging during silent watch, when the power draw must be provided solely from energy storage for extended periods of times (4 to 8 hours). Power supply must be delivered in two forms: continuous and pulsed. For a vehicle weighing about 20 tons, the continuous power ranges from 400 to 500 kW, which is supplied from the main prime mover, supplemented by 25-30 kW-hr of energy from a storage system. Pulsed power, however, depends on the loads and repetition rate.

Since electric power is used for continuous loads such as mobility, and also for pulsed loads such as electric weapons, it would make sense to have one common power and energy management system onboard the vehicle to distribute electric power to various users according to a defined precedence. Thus, a Combat Hybrid Power System (CHPS) program was introduced to evaluate such a power management and distribution system.

Enabling Technologies

The CHPS program was initiated by the Defense Advanced Research Projects Agency (DARPA) and continued by the U.S. Army RDECOM – TARDEC (Tank Automotive Research, Development and Engineering Center). The major goal was to design, develop, and test a 15-ton notional hybrid electric combat vehicle, incorporating all the power demand onboard a vehicle system, and assess the feasibility of simultaneous power distribution to propulsion.

In the course of designing the components for the 15-ton combat vehicle, some critical and enabling technologies were identified. They included high-temperature power electronics, high-energydensity and high-power-density batteries (namely Li-Ion batteries), and hightorque- density traction motors. To the extent possible, all the components and auxiliary systems had to be integrated within the space available in a 15-ton combat vehicle. Two technical challenges appeared: the amount of power needed for all the loads, and the size and weight of the components. A first estimation revealed that using state-of-the-art technologies would require at least twice the space available within a combat vehicle.

The most aggressive goals were set for the power electronics, the motor and generator inverters and rectifier, and the DC-DC converters, and also for the thermal management. Another aggressive metric was set for the Pulse Forming Network (PFN), which had to be reduced by more than half of its current size in order to install it in the vehicle. Improvement in both the power converters and the PFN hinged on the maturation of wide bandgap (WBG) materials such as SiC. This material provides the capability to build converters that operate at high temperature, high frequency (50-100 kHz), and higher efficiency.

Vehicle Mobility

In a combat vehicle, there are three main users of continuous power: mobility, thermal management, and silent watch. Power is supplied to most of the mobility and thermal loads from the prime mover (the engine), whereas the silent watch is solely supplied from the energy storage (a battery bank), which is also recharged from the engine driven generator. For optimum performance, the power is split between engine and battery for either best fuel efficiency or burst power, according to the specified vehicle duty cycle.