The SURUS platform includes two advanced electric drive units, four wheel steering, advanced propulsion power electronics, a lithium-ion battery system, a fuel cell system, and a hydrogen storage system. (image: General Motors)

TARDEC pursues advanced power generation

In the middle of a desert or other remote military zone, advanced power generation can keep the U.S. Army’s ground vehicles and combat support equipment ready for the demands of duty.

“Our power generation advancements are impressive in terms of the capabilities these technologies enable. The most exciting ground vehicle advancements, including driver-optional capabilities, are all enabled by the vehicle’s power structure, which in turn needs a strong, reliable, well-developed architecture,” Dr. Paul D. Rogers, Director of the U.S. Army Tank Automotive Research, Development and Engineering Center (TARDEC) in Warren, Michigan, said in an interview with Truck & Off-Highway Engineering.

One highly touted example of a robust vehicle architecture is the Chevrolet Colorado ZH2, engineered via General Motors in collaboration with TARDEC. Designed to perform in extreme off-road environments, the ZH2 is built on a stretched midsize pickup truck chassis that employs a uniquely modified suspension and oversized 37-in tires.

ZH2’s fuel cells generate electricity from a hydrogen source. That electricity powers the vehicle’s propulsion system and the onboard electronics, while off-vehicle power is provided via an Exportable Power Take-Off (EPTO) unit. The EPTO takes the high-voltage from the fuel-cell stack and converts it to both high- and low-voltage AC to power tools and other equipment.

According to Kari Drotleff, TARDEC’s Program Manager for Fuel Cell Technology, Ground Vehicle Power and Mobility, the ZH2’s exportable power ranges from 25 to 50 kW, providing the capability to power a mobile command center. The demonstrator truck has been undergoing field testing at U.S. Army military bases since April 2017.

“So far the feedback from our users, the soldiers, has been fantastic,” Drotleff said. The evaluations, which are slated to continue through the spring of 2018, address multiple considerations, ranging from acoustic and thermal signatures to stationary power generation.

Fuel-cell platform with autonomous capability

The follow-up to the ZH2 is the Silent Utility Rover Universal Superstructure (SURUS). This fuel-cell platform is envisioned as both a commercial- and military-use electric vehicle with autonomous driving capability. “TARDEC worked with General Motors to develop the overall vision of the SURUS concept vehicle, including its performance, weight, dimensional targets, and base architecture,” said Drotleff. The concept vehicle extensively uses off-the-shelf and near-term components and technologies.

With a hydrogen storage system capable of providing a driving range of more than 400 miles, SURUS is a prime candidate for field testing. “TARDEC and GM are exploring potential program options to take the SURUS concept vehicle and turn it into a functional demonstrator vehicle,” Drotleff said.

While the automotive industry typically uses nickel metal hydride or lithium-ion batteries to power the electric motors in hybrid-electric and all-electric vehicles, fuel cells are deemed a better choice for powering the electric motors in future military vehicle applications. According to Dr. Rogers, “With the weight of Army vehicles (an Abrams tank can push upwards of 80-ton) and the heavy power draw of our applications (drawing at times kilowatts of power), the power density with batteries just isn’t there yet. That leaves hydrogen tanks fueling fuel cells to generate the electricity.”

TARDEC engineers and researchers have been conducting exhaustive studies on the feasibility and practicality of portable hydrogen generation. Said Dr. Rogers, “In an Army where hydrogen fuels our vehicles, how do we get that hydrogen to the soldiers? Where does it make the most sense to generate it, and when does it make sense to transport or store the hydrogen?” TARDEC is working with technical specialists at the U.S. Department of Energy, the automotive industry, U.S. Army laboratories, and universities to develop solutions that meet the Army’s needs.

One potential problem-solver under review is a prototype fuel reforming system to generate hydrogen from JP-8 (jet propellant 8). The JP-8 fuel reforming system, which can be transported via a pallet system, was developed in conjunction with a mobile hydrogen storage and refueling system. “These prototype systems were built to support the ZH2 during its 2017-2018 evaluations,” Drotleff said. She points out that the SURUS platform--capable of carrying heavy equipment--could support mobile hydrogen generation, given its ability to produce onboard power.

600V electrical systems

Another technology poised to play a key role in solving the U.S. Army’s need for vehicle power generation is an Integrated Starter-Generator (ISG). “The Allison-DRS 3TIG design and development was successfully tested by TARDEC,” said Drotleff, adding that TARDEC also has a 160-kW generator under development with L3 Technologies. “That program is expected to conclude in fiscal year 2019,” she said.

Another piece of the power generation puzzle is the voltage system. A 600V bus electrical system means greater flexibility in standard architecture for mission equipment sets. In addition, all of the secondary equipment supporting that power infrastructure could undergo a dramatic weight reduction, providing more on-vehicle weight and space availability for mission-critical components. “As an example, the weight savings in the electrical cabling alone for a 600V system versus the current 24V system is extraordinary,” said Dr. Rogers.

A 600V electrical system is already a reality for a few of the Army’s newest vehicles. For example, the M109A7 Self-Propelled Howitzer is equipped with a 610V DC system; a full-rate production contract was recently awarded to BAE Systems.

In order to apply a 600V system to additional Army platforms, component size and weight reductions are needed. Silicon carbide (SiC) power electronics are likely replacements for today’s traditional silicon-based electronics. “The Zeus power inverter is an example of the size reduction SiC brings for a starter/generator inverter,” said Drotleff, noting that the Zeus can enable a 600V bus from the ISG.

In order to support emerging technologies, Drotleff said that a 600V system would be implemented on any new or modernized combat vehicle system.

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