John A. MacBain

Evaluation of SOFC Hybrid Systems for Automotive Propulsion Applications

The polymer electrolyte membrane (PEM) fuel cell is generally regarded as the fuel cell of choice for automotive propulsion applications. However, PEM fuel cell has several disadvantages such as the requirements of pure hydrogen, complex water management, and the hydrogen infrastructure. Despite having efficiency, cost, and fuel flexibility advantages, solid oxide fuel cell (SOFC) systems have not been considered for automotive propulsion, primarily due to the long start-up times of SOFC systems. Recently there has been some interest in using SOFC hybrids for propulsion applications. These hybrids are mainly: (1) a combination of SOFC and battery as a range extender type series hybrid vehicle and (2) SOFC and battery driving an electric machine combined with an internal combustion engine (ICE) driven system operating as a parallel hybrid vehicle. In this paper, a comparative study of the SOFC hybrid vehicle strategies for propulsion applications are presented, the performance of the systems are compared, and the feasibility and challenges are discussed

Full Vehicle Simulation for Series Hybrid Vehicles

Delphi and the National Renewable Energy Laboratory (NREL) collaborated to develop a simulation code to model the mechanical and electrical architectures of a series hybrid vehicle simultaneously. This co-simulation code is part of the larger ADVISOR® product created by NREL and diverse partners. Simulation of the macro power flow in a series hybrid vehicle requires both the mechanical drivetrain and the entire electrical architecture. It is desirable to solve the electrical network equations in an environment designed to comprehend such a network and solve the equations in terms of current and voltage. The electrical architecture for the series hybrid vehicle has been modeled in Saber to achieve these goals. This electrical architecture includes not only the high-voltage battery, generator, and traction motor, but also the normal low-voltage bus (14V) with loads common to all vehicles. The co-simulation version of the series hybrid model retains some of ADVISORs standard series vehicle model elements such as the mechanical drivetrain, the fuel converter, and the series hybrid control strategy. The electrical architecture is simulated in Saber, which is controlled via ADVISORs menu structure. ADVISOR communicates with Saber through a co-simulation arrangement, allowing a system-level solution to progress. The open code permits the end user to implement vehicle-specific series hybrid control strategies. This paper covers technical materials including: A brief overview of the co-simulation concept The electrical component and system models in Saber necessary for the series hybrid vehicle architecture The series hybrid control strategy used for co-simulation and its integration into ADVISOR Discussion of sample results from the co-simulation of ADVISORs baseline series hybrid vehicle Demonstration of the ability to co-simulate the propulsion and electrical systems for ADVISORs default series hybrid vehicle.

Logistics and Capability Implications of a Bradley Fighting Vehicle with a Fuel Cell Auxiliary Power Unit

Abstract : Modern military ground vehicles are dependent not only on armor and munitions, but also on their electronic equipment. Advances in battlefield sensing, targeting, and communications devices have resulted in military vehicles with a wide array of electrical and electronic loads requiring power. These vehicles are typically designed to supply this power via a main internal combustion engine outfitted with a generator. Batteries are also incorporated to allow power to be supplied for a limited time when the engine is off. It is desirable to use a subset of the battlefield electronics in the vehicle while the engine is off, in a mode called silent watch. Operating time in this mode is limited, however, by battery capacity unless an auxiliary power unit (APU) is used or the main engines are restarted. Integration of a solid oxide fuel cell (SOFC) auxiliary power unit into a military vehicle has the potential to greatly extend silent watch operating time and capabilities while significantly reducing fuel use. In this paper the results of a study are presented which show the fuel usage and capability impacts of incorporating a fuel cell APU into the electrical system of a Bradley M2A3 Diesel Infantry Fighting Vehicle. Several APU sizes are presented with varying levels of electrical equipment and engine-off capability. Complete off-loading of engine-driven accessories is also studied as a scenario with the resulting impact on available engine power presented. The silent watch operating scenario shows an 86% reduction in fuel use. With fuel costing several hundred dollars per gallon as deployed on the battlefield, such a reduction is valuable. Furthermore, the SOFC APU offers 36 days of continuous silent watch using the same JP-8 fuel tank as the M2A3 without the need for a secondary fuel supply.