Ultracapacitors and the Hybrid Electric Vehicle - Maxwell Technologies - #1

By Bobby Maher Director of Technical Sales, Maxwell Technologies Ultracapacitors

Due to the recent increase in worldwide gasoline prices, as well as ongoing public and governmental pressure for a more environmentally friendly and fuel efficient means of transportation, automotive manufacturers are developing product lines that incorporate true alternatives to the gas-powered drive trains that are the hallmark of the Industry.

These manufacturers' ultimate goal is to adopt fuel cell technology for all vehicle energy requirements. However, fuel cells are not likely to be ready for volume production for at least a decade. This is primarily due to the fact that while fuel cells are a promising technology, they also have multiple drawbacks which must be resolved before they can become truly viable. For example, the most common type of fuel cell being considered for the automotive industry Is a hydrogen/oxygen-based technology that uses hydrogen for fuel and oxygen from the atmosphere to create electricity. Although these fuel cells are efficient and dynamic enough for automobile use, there is no existing infrastructure for hydrogen delivery, nor is hydrogen easy to handle safely. Furthermore, hydrogen tanks tend to be large in volume and must be strong enough to withstand very high storage pressures in order to avert accidents. Similarly, metal-based fuel cells, which have also been explored for automotive use, suffer from an insufficient delivery infrastructure, a safety concern, and a large size and strength reguirement for the tank. Furthermore, when sized to deliver maximum high power loads, such as those required for engine starting and acceleration, fuel cells must become larger and thus, more costly.

Perhaps the most promising near-term alternative to fuel cell driven vehicles is Hybrid Electric Vehicle {HEV) technology. HEV technology combines the best characteristics of fuel-driven engines, electric motor drives, and energy storage components. It is designed with a combustion engine that functions as the primary power source, and an electric power storage system that functions as the secondary power source. The presence of the secondary power source allows designers to size the combustion engine for cruising power requirements. The secondary source handles peak power demands for acceleration. In addition, the secondary source is used for capturing regenerative braking energy and applying that energy for further acceleration or for the basic energy needs of supplementary electrical systems. Through this basic design structure, HEVs promise to offer low maintenance, clean operation, and high fuel economy.

But while many manufacturers have made progress in HEV control, engine, and motor design, they have not been as successful with regard to the electric power storage systems used as secondary power sources. This insufficiency has primarily been due to the fact that batteries are used to provide electric power storage in most

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