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Electronics power systems in automotive applications are undergoing a massive change. Firstly, the transition from internal combustion engines to electric, fuel cell, and hybrid power is gathering momentum.
At the same time, cars are becoming more sophisticated, evolving towards an intelligent electrically-powered platform with many more electronic subsystems and accessories—requiring a substantial increase in the need for electric power.
Electric and hybrid vehicles have been under development for years, but have mostly failed to become widely adopted, with the exception of Toyota's Prius. There have been fundamental problems of energy storage and delivery that have yet to be successfully and cost-effectively overcome. Many of these issues are due to the limitations of batteries—heavy, large, with a limited charging rate and potentially high maintenance.
Recently, newer designs have taken advantage of the benefits of another component: the ultracapacitor. Integrating ultracapacitors with other energy devices solves many challenges that are not solved efficiently using a single device. For example, combining high-energy lead-acid batteries and ultracapacitors can create a system that has the excellent energy, self-discharge, availability, and low cost associated with lead-acid technology, and the high charge acceptance, high-efficiency, cycle stability, and excellent low-temperature performance of the ultracapacitor.
Ultracapacitors can also play a valuable role in distributed power systems, thus simplifying the wiring required and reducing cost.
Power train applications
System design engineers can take advantage of the power of ultracapacitors to conserve energy by allowing the engine to stop while the vehicle is stationary, and then to be restarted nearly instantly on "tip in" of the throttle. Ultracapacitors also allow regenerative braking energy to be captured, thereby significantly increasing efficiency and reducing pollution. The use of engine start/stop and regenerative braking has been estimated to produce between 7 and 15% increased fuel efficiency while reducing pollution by even more.
Announced programs for integrating ultracapacitors into vehicle power trains include BMW, VW, Honda, Nissan, and Toyota, among others (see below). These vehicles run the gamut from concept to production-intent, and include systems for hybrid trucks, buses, and passenger vehicles.
Raymond Freymann, the managing director of BMW Group Research and Technology, has also indicated that BMW is working on a gasoline-electric hybrid, using ultracapacitors boosted by regenerative braking, rather than batteries. He has been quoted recently as saying, “[The ultracapacitors] are lighter and store less power, but unlike batteries we can use all their power. An electric motor has a lot of torque at low revs—that is its main benefit—so it's ideal for fast initial acceleration. At higher revs, once you've begun to accelerate, nothing can beat an internal combustion engine. Our hybrid approach combines the best characteristics of both engines.”
Battery problems in hybrid vehicles
Let's look at Hybrid Electric Vehicle (HEV) technology, which combines the best characteristics of fuel-driven engines, electric motor drives, and energy storage components. 
Mild or full hybrid vehicles have a combustion engine that functions as the primary power source, and an electric motor with a power storage system that functions as the secondary power source. Designers are able to size the combustion engine for cruising power requirements thanks to the presence of the secondary power source that handles the peak power demands for acceleration.
Additionally, regenerative braking energy is captured by the secondary power system, and that energy is applied for further acceleration or for the basic energy needs of supplementary electrical systems by using the secondary source.
Mini hybrid vehicles use a power generator that delivers the power required to handle start/stop idling only. Finally, in the micro hybrid concept, there is a power generator and power energy storage source to handle start/stop idling, fuel consumption reduction due to energy recuperation/acceleration assist, and to power some additional features like fast windshield heating.
Using only batteries to provide the electrical power storage has drawbacks in the hybrid applications.
Batteries have difficulty functioning in cold weather.
Batteries require a sophisticated charge equalization management.
Batteries have limited cycle life under extreme conditions, which results in cost replacement throughout the life of the vehicle.
Batteries are limited in their ability to capture and provide bursts of high power during short duration events such as acceleration and regenerative braking, which reduces the efficiency of the hybrid electric drive system design.
Ultracapacitor features
Ultracapacitors can fulfil many of the functions of batteries in this application, but with dramatically higher reliability and overall performance. They significantly improve power management in hybrid electric vehicles and extend battery life. In addition, ultracapacitors allow for lower emissions, better fuel-efficiency, and advanced electrical drive capabilities.
Redesigning a power system to use ultracapacitors can allow the HEV to more efficiently recapture and reuse braking energy. Compared to conventional diesel engines, reduction of fuel consumption is estimated at greater than 50%, reduction in particulate emissions is greater than 90, and reduction of nitrogen oxide emissions is 50%.
Looking beyond hybrid vehicles, another example where the ultracapacitor has a valuable role is in designs based on a fuel cell. Even though the fuel cell is capable of being dynamic enough to handle transients, it is large and costly if sized to meet the maximum load. Therefore, it is more cost-effective to have a hybrid design with a fuel cell and a bank of ultracapacitors, which can handling very dynamic loads such as initial acceleration and absorbs braking energy.
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