Ultracapacitor System Design: Optimizing Hybrid Electric Vehicles with Fuel Cell Power - Maxwell Technologies - #1

By Richard E. Smith Sr. Vice President of Strategic Business Development, Maxwell Technologies

The automotive industry's recent push towards developing electric and hybrid electric vehicles (EV and HEVs) is a direct response to the growing global pressure to improve the environment and has resulted in a search for significantly cleaner and more efficient vehicles. So far, the outcome of this search has not been entirely promising, as the success of these new, environmentally friendly vehicle architectures depends on the development of advanced energy storage technologies. Among the many options explored, fuel cells have been identified as having a good potential for use as the primary source of power train energy. But since internal combustion engines and fuel cells have significantly different characteristics, few current automotive designs can immediately replace conventional power trains with fuel cells alone.

However, the promise of fuel cell technology has had a recent resurgence due to new advancement - not in fuel cells, but in another power technology: the ultracapacitor. Indeed, high power energy storage is required in all types of fuel cell applications and ultracapacitors are ideally suited to provide it. Moreover, ultracapacitor technology and cost reductions have advanced significantly in the last few years, driven by the need to develop components for the consumer electronics industry as well as the new EV and HEV markets. These improvements, as well as the unique characteristics of ultracapacitors, open up opportunities for the development of new power train and subsystem architectures - utilizing both ultracapacitors and fuel cells - which can improve performance, efficiency, and cleanliness in EV and HEV technology.

Hybrid applications with ultracapacitors and fuel cells use two different power sources to solve two different power requirements. The fuel cell, which acts as the primary power source, is sized for the continuous load requirement. The ultracapacitor, which acts as the secondary power source, is sized for the peak load requirement. In some cases, the peak load is satisfied by only the second source, and in other cases, both the primary and secondary sources are required. But because of the wide variety of driving profiles, the selection of the power ratio between primary and secondary power sources is a matter of judgement. Nevertheless, system architectures that optimize the balance of power and energy between fuel cells and ultracapacitors will be significantly cheaper and more responsive than fuel cells alone since fuel cell power trains are well suited to take advantage of the ultracapacitor's unique characteristics.

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